Small 12/24 Volt System Performance




1. Danfoss Compressor runs too much


2. 12 volt cycle times Question 


3. 12/24 volt boat refrigerator’s Poor performance possible causes


4. AB poor performance or not?


5. SunFrost R19 refrigerator poor performance


6. SCM Poor performance


7. Engine drive and BD35 Hybrid System Performance


8. Spillover poor performance box too large for compressor


9.  RV Cabinet Refrigerator performance installed in Boat 


10. BD35 Performance  Bad idea to add refrigerant


11. Performance reporting Details


12. BD50 with poor performance.


13. Cool Blue performance


14. AB Poor performance Will not Cycle Off


15. New Isotherm Performance


16. BD Thermostat performance


17. New Adler Barbour Problems


18. Tropics versus Cold Climate refrigerant performance.


19. Poor Performance Frigoboat


20. Adler Barbour Power plate Performance


21. Old AB Question about its performance.


22. WAECO BD return line condensate affect on performance



1. Danfoss Compressor runs too much


I have an Adler Barbour refrigerator on my sailboat. It is probably 12 or 13 years old. I leave it on essentially all the time. In the last several months, it seems to run nearly all the time (it does occasionally shut off). Other than that it works well, but I am concerned about the draw on my batteries and the battery charger. I would appreciate help in trouble shooting this problem. Thanks.

Answer: This is a frequently asked question. Refrigeration performance over time can change due to low refrigerant flow, poor condenser cooling and increased refrigerated box heat load.

Condenser Cooling: Is the number one cause of poor performance on refrigeration units like Adler Barbour’s (AB) Cold Machines.  The condenser’s cooling medium’s passage ways need to be cleaned at least once a year or more frequently if it is a live aboard boat. Abler Barbour’s cold machines, over the years, have several configurations of fan cooled condensers. Earlier AB units had a fan behind the condenser and no shroud. Next, came fans with a shroud in front of the condenser which made it easy to remove, allowing access to vacuum dust and hair from condenser cooling fins. The next series of AB condensing units mounted the fan inside the shroud which was riveted to the condenser coil, this required removing rivets to gain access to clogged cooling fins.

There are two indications of poor condenser cooling High amperage draw and when the liquid refrigerant line from condenser towards evaporator is warmer than 110˚F.

Low refrigerant flow: is critical on these small AB units, plus or minus ½ ounce of refrigerant will affect performance. Too much refrigerant will create high pressure and high amperage. Not enough refrigerant will reduce cooling capacity. You can check for correct refrigerant flow by viewing the frosted areas of the evaporator and the frost on the return line from evaporator towards compressor. A properly serviced AB with an aluminum thin plate evaporator will have frost covering 95% of its surface area and no frost on the line outside refrigerator.

Increased heat load can be caused by climate condition changes with ambient air and seawater, air infiltration from door or lid seals, and condition of aged insulation. One way to visually check lid and door seals is by closing them on a thin ribbon at many points around their surface. If ribbon pulls out easily the seal is not compressed enough. Condensation on an exterior surface is the best indication of air leakage or lack of insulation. A well insulated box should not develop condensation on the exterior surface of the insulation. Condensation will form on exterior surface of insulation when ambient air temperatures are 8 to 10˚ warmer than exterior surface temperature of insulation. I believe that a 4˚ Delta T or less is the correct exterior difference for pleasure boat insulation.  Insulation that is over ten years old may or may not have dried out allowing the insulation’s many closed cells to open and release the inert gas that is the true non heat conductor. Over time, as the refrigerator cycles, warm moist air can enter insulation cells that have out-gassed leaving moisture as a heat conductor inside the open cells as air moves in and out of each cycle.


2. 12 volt cycle times Question: Is there a "standard" cycle time for an AB refrig? I don’t know if mine is cycling too much or not enough.

Answer: The answer is, NO. Best guess answer to the question is if the compressor runs less than fifty percent of the time, running at its slowest speed, and the box is maintaining desired temperature it is efficient. Older BD2.5 and BD3 compressors run at fixed speed cycling depending on the box’s hourly heat load. If they cycle too often 6 to nine minutes of compressor running energy is lost with each unnecessary cycle.

There are many factors that affect number of compressor cycle times per hour:

Super and sub cooling of high pressure gas is either too much in cold weather or poor condenser cooling in warm weather.

Incorrect refrigerant charge.

Ambient temperature change.

Poor insulation.

Moisture in insulation.

Thermostat setting.

If the unit has a BD35 or BD50 compressor, it will be less than 10 years old  and its compressor speed can be set too high or too low wasting energy.

To assure yourself that this system is operating correctly, check to see that the thermostat is installed correctly per manufacturer’s instructions. The thermostat’s temperature sense tube must not touch the evaporator anywhere except where it is designed to be clamped. After the unit has operated for at least one day with the thermostat set at mid range there must be frost covering at least 90% of the evaporator’s surface area and no frost on the return line( the outside refrigerated area on line returning to compressor.) Make sure the condenser airflow is adequate and warm heated air is not passing through the condenser a second time.

If you are satisfied with the refrigerated box’s maintained temperature and if the compressor cycles twice an hour and runs less than 50% of the time, you are getting good performance.

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3. 12/24 volt boat refrigerator’s Poor performance possible causes


Comparing a boat’s ice box conversion unit’s performance to a home refrigerator or even to an older boat refrigeration system is a mistake. A home refrigerator is designed around a cabinet size with each component selected to collect and dispose of a given amount of heat energy. Home refrigerators are also assembled, serviced and tested in a controlled environment your boat’s ice box conversion unit is not treated with the same quality control; this is why performance varies from one boat to another.

Small 12/24 volt ice box conversion units in the past were advertised so the consumer would believe one unit could be efficient in various size boxes. In the last 10 years when buying a 12/24 volt conversion refrigeration unit, there are over one hundred options to choose from, such as compressor size and speed selection, evaporator size and type, to various heat removal mediums. A small conversion refrigeration unit will be efficient and perform properly only when the right unit is selected and installed correctly with sufficient insulation to deliver the desired box temperature in a planned geographic cruising area. The causes of poor refrigeration performance can usually be corrected by first identifying the deficiency and correcting it. If a refrigeration system satisfies the desired temperature in the box, its performance is good but if the daily power consumption is higher than expected, then conditions that affect short run times or long run time high pressures, need to be investigated.

The most common causes of poor performance on small 12/24 volt refrigerator are:

• Poor airflow through condenser.

• Condenser fan is not shrouded.

• Heated air that passes through condenser is allowed to pass through it again. Air            cooled condensing units are designed to be efficient when boat’s interior ambient          air temperature is between 70 to 90˚F.

• On units cooled by water, poor or excessive water to refrigerant heat transfer    will lower overall performance.

• Compressor cycles off and on too often.

• Too much refrigerant, this is even possible on a new unit.

• Small amount of refrigerant was lost on installation of line connectors or the    system has a small leak.

• Thermostat incorrectly installed.

• Compressor speed too fast or too slow.

• Air or incorrect gas mixture in refrigerant.

• Very old box insulation or when insulation is wet or VIP insulation has failed.


Common misunderstandings about small 12/24 volt boat ice box conversion refrigeration units:
           • That most refrigeration mechanics know how to correctly service them. They   don’t.
           • The shorter the compressor run time the more efficient the system is.  Not true,          On variable speed models they will run longer and are more energy efficient when    running at a slower speed.
           • Poor refrigeration performance is generally related to lack of insulation, NO but            high energy consumption might be linked to lack of insulation.
           • A holding plate with less surface area than the recommended size of thin plate            evaporator is not as efficient as the thin plate evaporator and may also result in   poor performance and high daily power consumption.
           • Water cooling a small 12/24 volt unit will provide better performance than air   cooling, only true in rare cases and never more reliable than air cooling.

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4. AB poor performance or not?


We have lived on the boat for a month now and as we fix it up and I have noticed the fridge cycles on about every 10-15 minutes no matter what I have the thermostat set to. If I have it set to a warmer temp it runs less- which makes sense but I am trying to figure out why it turns on so often. Then lately it has had trouble starting up. I read the manual and deduced that it was the Fan Circuit Limit because when I unhooked the secondary/ optional fan that someone added to the outside of the unit it started up fine.  

I cleaned the connection and it appears to be working, but still cycles on every 8 minutes, runs for about 8 minutes then off for 8. And right now the ambient temperature is about 50 degrees on my boat so I don't think it is an insulation issue.

I am wondering if the previous owners installation of the second fan has done more harm than good.

He bent a bunch of the smaller cooling coils when he jammed two zip ties through them. I have taken them out and rerouted them to the outside coils.

Also wondering on an older unit like this does it make sense to have the refrigerant checked and added before I take off for a cruise? Or if I get a new compressor like the Danfoss BD50 F could that work with my existing pipes and evaporator? 

Can I check and add refrigerant myself, my neighbor has a gauge ? If not can you recommend someone in the Titusville area of Florida, of if you are heading up this way we'd love to work with you on this one. 

Answer: If the electronic module was in the picture I could tell what compressor you have. Whatever you do not allow ANYONE to connect gauges to this system.

It is obvious from the picture that airflow through the condenser is blocked and the fins need cleaning. Look behind the fan.

Eight minutes running and eight minutes off demonstrates ACCEPTABLE performance if desired box temperature is maintained.

Your refrigeration unit was serviced to operate in ambient air temp of 70 to 90˚ F. When the condenser’s cooling medium air is over 70˚ a perfect refrigerant charge will be indicated by frost covering 95% of the evaporator’s surface area and no frost on line returning to compressor.

If you have a well insulated box of three cu ft or less a variable speed BD35 or BD50 compressor would be 20 to 50% more energy efficient. Four cu ft or more boxes, in warm climates, do not demonstrate sufficient energy savings to justify replacing older  BD2.5 or BD3 units with newer variable speed units.

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5. SunFrost R19 refrigerator poor performance.

I have a Sunfrost RF-19, and it has always had water condensing in the fridge section. It's especially bad in the summer. I purchased it 5 years ago, and would never buy another one. Recently the latch broke and we held it shut with a bungee cord. I don't think this condensation is an inevitable trade off for efficiency. I attribute it to poor design, with the ineffective door seals. Do you ever have any problems with water collecting in the bottom of the fridge? Mine has done it from day one.

Answer: I have not seen a Sunfrost refrigerator but I am familiar with the Danfoss BD35 compressor. This compressor’s Btu output capacity is small for that size refrigerator in a warm climate. It is normal to have a thin frost cover on 100% of the evaporator’s surface. If there is an area of an evaporator that does not have frost on it, this generally means lack of refrigerant. The thickness or volume of frost is a result of moisture in the box. Frost on an evaporator thicker than ¼ inch will reduce the system’s performance. The primary reason for frost is the moist air infiltration when the door is opened or through a leaking door seal. Door seal must be held in tight contact all the way around the seal. To test the door seal, close the door on a thin ribbon. If ribbon is easy to pull out, that area of seal is not compressed by the door. One performance improvement might be to increase airflow across condenser.

I found the information below on the web regarding your unit:


I'm thoroughly DISAPPOINTED with our Sun Frost. I've replace the gaskets 2 (some 3) times. And still we don't get a good seal. One of the Freezers runs incessantly. There is always a build up of frost. (Indicative of air leakage). Half of the catches have broken. I've used the things less than 2 years. I quit replacing the gaskets with what SunFrost provides. They are just not temperature stable. SunFrost's gaskets shrink too much in cold, and then leak @ the corners

Richard, thanks for responding to my question. The refrigerator that this compressor is in has been in use for several years. (We actually have 2 of these and am currently focusing on this one) It is a Sun Frost R19 refrigerator and is having difficulty keeping the temp in the refrigerator at a useable temp. When the refrigerator is being used frequently – opened several times a day, it only cools down to -45-50˚ F. However the inside-back of the fridge is covered with frost and has frozen things against the back wall. We defrost the fridge weekly. The fridge has been working marginally for about the last year. I have replaced the seal on the door to make sure that this is not the problem. I had the repair guy come out thinking that I would get a “recharge”. He said a recharge wouldn’t do any good and he measured the pressures on the system and said that the pressure on the secondary circuit (I assume this is the condensing side of the coils) was too high indicating that the compressor wasn’t working as well as it needs to be. I don’t believe that any refrigerant has been removed, let alone dehydrating the system. The frost is not in a particular shape – rather covering the entire back wall. I have not measured the current draw of the compressor  I will do this. The access to the cooling coils (cooling tubes) is on top of the fridge and they are clean and free of obstructions.

Any help you can provide is very welcome! I really don’t want to replace the compressor if I don’t have to. I did think of adding a resistor to the control to increase the compressor RPM thinking this might help.  Since I have this similar problem with both my SunFrost units I am trying to figure out what needs to happen. I did buy a new DF35F compressor and coil system on Ebay – didn’t have any control electronics with it.

We live in the jungles of Hawaii and have a pretty normal ambient temperature of about 80˚F. during the day.

Subject: 101N0200 with new DF35F compressor


I saw your post on Rparts web site and can not believe the compressor is bad. I assume the unit worked well before, then quit cooling and no one added or tampered with the refrigerant before this service guy? Did this guy remove refrigerant and dehydrate system with vacuum pump? Describe the area frosted in detail is there frost on line outside box toward compressor? Do you know how many amps this unit is drawing? Have you or did the service guy clean the intake air inlet and inlet fins to condenser? Is the fan drawing a good flow of air?

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6. SCM Poor performance

I installed an Alder Barbour Super Cold Machine in my 42 ft sailboat Dec 2007
Compressor Cu 200, Large Evaporator Box VD-152
Box installed in Freezer side 3.5 cu.ft spillover fan to fridge 4.5 cu. ft. Total max 8 cu.ft.
Very well insulated Equivalent 8-9 " Distance between compressor in cockpit locker to fridge approx. 15 ft used every inch of line that came with pre-charge system.
System worked good for 4 months in 2008 and couple months in 2009.I returned to Brunswick Ga in Jan. 21,2010 where I keep the boat in water, I had been away for 9 months, The refrigeration system was shutdown during my absence. For the first 4-6 weeks all ok. Freezer side 17˚F at minimum cool setting of 1˚on Analog dial 0 to 7 coldest. Fridge side 45˚F fan cycling on/off as needed. Then we had 2-4˚nights where ambient temps dropped to approx.28-29˚ F. Shortly after this I noticed system running 100% of time ( 24hrs a day x 7 days ) Although outside avg day temps were 45˚F, I  knew system should not operate 100% of time, have digital inline ammeter indicated 3.0 Amps, normally 6.5 A @ start then drops to 5.5-5.8 A.  Based on my past experience with this system I thought it was low on refrigerant, therefore added a little R134A to suction side 4 times over a period of 2-3 hrs each time allowed Evaporator box to reach 75˚ F approx. before adding and allowed ample time between changes. Finally at start-up amps were approx 7 at start up then after running for sometime it dropped back to 6.5 A approx.

Not 100% sure but think suction pressure @start was approx 56 lbs, did not check suction or high pressure side after running , monitoring amps seems to make sense, temp in evaporator box dropped down to 17˚F and compressor cycled on-off with setting of 1 again. Everything was good for about 2 weeks then one morning I noticed freezer side was 45˚F ice cube trays were water, system running 100% of time 2.5 -3. amps.

Couple other things I noticed today if I allow compressor to run continuously amps will eventually drop to 2.- 2.5,-- sometimes when I shutoff electrical breaker and turn back on amps start at 5 then over 5 mins drop to 3.0. evaporator box gets a little cold but only 5-10˚F below ambient,.... also noticed both the copper suction and discharge lines 24 inches (approx.) from compressor are black not sure if this is something new or normal as not an area I can normally see, other area of the lines I wrapped with foam pipe insulation, more to protect them from chafing on anything.

 Not too sure what to do at this point. To me it appears the system is blocked and not circulating, no hissing or gurgling at Evaporator box. Tried bleeding both sides a little but does not seem to make a difference. Not too many Marine refrigeration guys in this area and to remove all and send back to Alder-Barbour would be a bear as I have to take half the boat apart just to get the Evaporator box and 15 ft of tubing out + it is out of warranty so don’t think Alder-Barbour/Waeco will be in a hurry to help. Did not see anything else in book that I should check.
Any ideas ,suggestions U can give will be greatly appreciated.
           Answer:  When the ambient air is colder than 70˚F the normal amperage will drop from 6.5 to maybe 4.5. The efficiency of compressor is very poor at low condenser temperatures. At 32˚ these Danfoss compressors stop running. To correct for low temperature conditions never turn water pump on SCM ON. To correct for low temperatures, cover part of air condenser with cardboard. Never allow anyone to connect gauges to one of these systems unless refrigerant loss is confirmed by other means. Very few service techs are careful enough to service this system. In order to service correctly for normal temperature ranges, the manufacture provides the correct volume by weight on this unit. My guess is 110 grams. Because this system held pressure for more than a year and the aluminum evaporator is not old enough to have leakage due to corrosion I would guess tampering with refrigerant started the problem. There is a procedure for servicing one of these units in the field when ambient air temperature is between 70 and 80˚F. From latest amperage figures it sounds like refrigerant and maybe the ester oil is now contaminated by air and moisture. These units have a very small filter dryer that already contains moisture when it leaves the factory. Connecting gauges that may have a small amount of moisture in them will over load system dryer. One small drop of moisture will plug capillary tube when it is exposed to temperatures below 32˚. Ice in cap tube will melt and refreeze controlling evaporator temp at 33˚F My recommendation at this point:

Pressurize system and leak test it with compressor turned off. Do not leave gauges on system after leak testing and make sure service caps have seals inside.

Dehydrate system with refrigerant vacuum pump for four hours while heating complete system to 100˚F.

With system and air temperatures at 70 to 80˚F, service with 134a refrigerant till amperage is stable at 6 amps. Wait 30 minutes and check frosted areas. A correctly charged system will have 96% of evaporator’s surface covered with frost and no frost on return line outside refrigerated box. As plate cools amperage will decrease.

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7. Engine drive and BD35 Hybrid System Performance

I hope you can shed some light on this problem, I'm stumped. System history: started life as an old technautics 110v/12v combo. Now running engine and DC compressors. Engine side is non-problematic. DC configuration has been upgraded to new bd35 compressor. New dual evaporator coil plate and TXV's (13x24x4). 3.5 reefer / 2.5 freezer cu ft spillover box with mix of blueboard and glacier bay ultra R (r-50) panels. Insulation is 12yrs old. Boat has been in the equatorial tropics for 8yrs. My troubles began when the original cold plate developed leaks in the evaporator coils. I pulled the system apart (both engine and DC) and first drained the plate looking for any traces of oil. Found none. I then drained the oil out of both compressors looking for signs of water ingress / emulsified oil etc. Found none. Note- very little oil was recovered from the DC compressor. No oil was recovered from the corresponding evaporator coil in the plate. Added an ounce of oil to the Danfoss when reassembling the unit. All the refrigerant lines to the box were also clear of foul oil or any sign of moisture. The new plate had the refrigerant lines and TXV's plumbed at the back of the plate, whereas the old one had them plumbed at the bottom rear. I had no choice but to replumb the lines on the new plate to match the lines coming into the box. Added 6"-8" of copper tubing to each line with requisite 90˚ elbows etc to facilitate this. Everything hooked up, leak tested, vacuumed and charged with R-12. (I'm in Micronesia) Engine side is fine. DC side pulls freezer down to 20˚ and then stops regardless of how long the compressor runs. Lo side is 0 psi hi side varies with ambient between 115 and 130. Ambient 88-94˚ F. I opened up the superheat 1/2 turn ccw. I could now see frost on the lo side line coming out of the plate. Lo side 1-2 psi hi side 115-125. Box pulled down to 18˚ overnight. Further opening of the TXV yielded no efficiency gains. I stuck masking tape to the plate and box sides to check temps with laser thermo: plate 6˚, box sides were about the same temps all around ~ 8-10˚ above plate temp. Box holdover I can't compare, boat is out of the water, the freezer is against the hull and in direct sunlight in the afternoon hours, and the box is empty. During the afternoon the box will actually gain a few degrees even if the system is running. But it seems that overnight the system should pull way down, still we seem to hit a wall at around 18˚. Box loses about 1.5 deg / hour when the hull side is not in the sun. I'd really appreciate any insight you may have. Thanks.

Answer: To summarize - Present system is hybrid with Technautics engine drive and a 12 volt condensing unit powered by a BD35 compressor. Both systems are independent of each other except they both have their own evaporator coil inside a 3 to 4 gallon eutectic solution holding plate. Refrigerated box is 6 cu ft spillover, 3.5 cu ft refrigerator 2.5 freezer. Insulation is 12 years old Blue board and Glacier Bay VIP ultra advertised to be R50 panels. Boat located in tropical conditions 88 to 94˚F.  If your insulation only had an R value of 20 you would need 5000 Btu of refrigeration daily. When freezer side is against the sun, the box loses 1.5 degrees per hour. Engine Drive is fine but 12 volt compressor only pulls freezer down to +20 degrees no matter how long compressor runs. With compressor running overnight freezer temp only drops to +18˚

Concerns about system application design.:

          With the poor reliability of VIP panels in marine applications is it possible one or more of these panels failed due to vacuum being replaced by moist air? A simple test of insulation’s adequate R value is to check its exterior surface temperature when box has operated at desired interior temperature for several hours. If insulation’s exterior surface temperature is more than 4 degrees colder than cabin air temperature it has low R value, if greater than 7 degree differential, condensation will form indicating very poor insulation.

          Selection of a condensing unit with a BD35 compressor for a 6 cu ft spillover box to be operated in tropical weather was a poor choice. Do you know what speed your compressor is set to run at? At maximum rpm your 12 volt BD35 unit is trying to freeze a 6 degree eutectic solution to a block of ice and will only produce 186 Btu per hour at 2000 rpm and 293 Btu at 3500 rpm compared to engine drive’s output of 3,000 to 6,000 Btu per hour.

          Holding plates are not efficient evaporators, their only purpose is to store surplus energy, if there is surplus energy available. Say the eutectic solution in your holding plate is set to freeze at +6˚F it then will take a temperature of -14˚F inside the plate’s 12 volt system’s evaporator coil. As evaporator coil cools to very low temperatures or -14˚ the Btu output of compressor decreases to 78 Btu per hour at 2000 compressor rpm and 122 Btu at 3500 rpm. These thermo inefficiencies inside holding plates when supported by very small compressors account for plate and box temperatures reaching an equilibrium with compressor output before desired box temperature is reached.

          You indicated that there was a TXV installed in the 12 volt system I assume there is also a liquid refrigerant receiver also in this system. Superheat control within holding plate evaporator coils depend on having reserve refrigerant to expansion valve when TXV is wide open and less when valve is restricting flow at low temperatures.



           Check condition of insulation.

           After unit has run for a couple hours open TXV to obtain 4 psi of suction            pressure

           Confirm compressor speed by checking resistance of thermostat wiring.   Disconnect thermostat wires T and C from module and measure resistance     of thermostat loop, no resistance will produce 2000 rpm 1500 ohms          resistance produces 3500 rpm.

           Box full or empty has no real affect on this problem, another Old cook’s tale. I have one on my test stand with BD3 and holding plate setting in          open 81 degree air shop and it will lower inside plate temp to -10 degrees    if left to run over night..

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8. Spillover performance box too large for compressor


I recently bought a sailboat with the intention of a world Pacific (Bora-Bora) cruise in three years from now. Unhappily the owner had died before I bought the boat so nobody can give me information on its use. The boat came equipped with a Danfoss BD35 with keel water cooled. It has an evaporator in an L shape of 30'' long that turns 90 degrees and prolong 12'' more for a total length of 42''.The evaporator is 12'' high. The box is 9 cubic feet and includes a 2'' divider in the middle 2'' in height smaller so the air could flow from one compartment to the other. My question is: Does this set up act as a freezer on one side and refrigerate on the other side or is it only a large reefer?

Should I modify it to have 1/3 freezer and the rest fridge by moving the separator towards the evaporator. How close should the food be to the evaporator to have a good heat transfer and stayed frozen. Would it be a good idea? Is it better to change the evaporator for a square one instead of an L shape one?

I have a 1200Amps battery bank, a wind generator, a 110Amps alternator and thinking about solar panels.

The box is urethane sprayed 5'' insulated factory made. I intend to add a 1'' polyurethane panel (instead of Styrofoam) wrapped in plastic and a 1'' bubble heat shield. How does it sounds?

Answer: Your BD35 compressor and L shaped evaporator will do a reasonable job in seawater temperatures of 65 to 75˚ F. A nine cu ft combination box is too large for the small BD35 compressor when cruising in tropical waters. Spillover icebox conversions generally provide only short term frozen food storage. The closer the frozen product is to the evaporator the longer it will maintain its quality.

Adding insulation to outside of box will not improve energy performance but adding extruded polystyrene (Moisture Resistant) insulation to box’s interior will, as it makes box smaller.

If I were you I would use present box as a refrigerator cooler and buy a portable freezer like the ENGEL 45

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9. RV Cabinet Refrigerator performance installed in Boat 


I hope you can help me with some advice.
I've recently bought a boat with a Novakool RFU6200 installed (2 door upright).
In hot weather it runs constantly and has problems keeping things cold.
Part of the reason is that there is not much venting so I'm going to cut a few more holes and install a fan to push cold air over the back of the fridge.
Just now when I pulled the fridge out of the cabinet I noticed that the pipe which comes out the top of the DB35F compressor and runs to the evaporator plates in the fridge and freezer has ice on it. The rubber which goes around the section of pipe (1' out of the compressor) has ice build up on it, which then melts when the fridge cycles off and then re-freezes. Do I need to cut the insulation off and reinsulate this section of pipe? Or does it indicate another problem?

Also I thought of a few other potential improvements but am not sure of their value.
1 - install a digital thermostat to give more precise control
2 - there are air voids in the cabinet on the sides and top of the fridge. Would     filling these voids with foam insulation help ie reduce chance of warm air pockets +     improve insulation of fridge?
3 - replace the power module with one of the Danfoss AEO units?

Answer: If you put a refrigerator designed for the RV industry in a marine environment its performance may be compromised. You did not say where boat is cruising but if the ambient air temperature is much above 75˚F a two door six cu ft refrigerator with a BD35 compressor is not going to demonstrate great performance. 

The only information you provided that indicates a correction is needed is it has problems keeping things cold. If the compressor never cycles off and the box isn’t getting cold enough, has nothing to do with the thermostat. Knowing what the compressor’s preset speed is would help. You can contact the factory and find out the compressor’s current speed or check resistance of the thermostat’s wiring circuit. With no resistance in the thermostat’s circuit, the  compressor would run at 2000 rpm if there is 1500 ohms the compressor is running at max 3500 rpm.

Compressors that run continuously under load would indicate poor condenser cooling which produces high side pressure. High liquid line pressure on these small capillary tube systems tends to decrease evaporator efficiency by moving refrigerant heat absorption beyond evaporator forming frost on line returning to compressor.


1 - Install a digital thermostat to give more precise control?

Your unit is designed to operate correctly with the thermostat it has. A digital    thermostat would be a mistake.

2 –There are air voids in the cabinet on the sides and top of the fridge. Filling     these voids with foam insulation might help by reducing the chance of warm air       pockets + improve insulation of fridge.

3. Most of the cabinet refrigerators have poor control of the condenser’s cooling medium. Some of these units use static air’s natural movement up back of cabinet            to remove process heat others use the metal of the cabinet to dispose of heat. I am    guessing your unit has a fan cooled condenser and either it is full of dust or its air         deflecting shroud is not designed to properly dispose of the condenser’s heat. The         best way to improve your unit’s performance is to find a way to better control          waste heat disposal.

Added insulation is required only when box’s exterior temperature is more than 4            degrees colder than ambient air surrounding refrigerator.

4. Replace the power module with one of the Danfoss AEO units.

5. Investigate the current compressor speed first and with energy already being   wasted as indicated by frost outside refrigerated area I would spend my time on       improving condenser cooling and Door Seal contact.. Also See section on Nine Ways To Use Fans.

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10. BD35 Performance  Bad idea to add refrigerant


Last year with your book as a reference and your answers to help, I installed a new quick connect to both my A-B compressors- both BD3 with R134a, and recharged to a 5.5A current draw after 20 minutes with pure R134a. I never ran the freezer very much last year after recharging so I don't have good performance data on that unit, but the refrigerator ran much better with adequate cooling and reasonable power consumption.

This spring, the initial current draw was in the 4-4.5A range on both the refrigerator and freezer compressors. Frosting of the cold plate seemed to take a long while also.

Reviewing my data, that I recorded last year at recharge, it appeared that the low initial current and up to 20 minutes was likely due to a slight R134a loss.

I then added a very small amount of R134a to both the refrigerator and freezer compressors being careful to purge the charging hose each time. I added small spurts until the current draw at 20 minutes was between 5-5.5A.

Now I am on a four week cruise and the power draw of these two units seems excessive. Overnight I measure the power draw to be about 60AH for 8 hours. The refrigerator temp is holding about 35F and the freezer temp is between 11-19˚F.

I think the refrigerator is running fine, but the freezer is my concern. It seems to run for long periods even when the temp is at 11˚F. The current draw at 11˚F is 5.2A. The thermostat setting is at 4. The inlet connection and inlet line (about 20") are all frosted within the box. The connection to the return suction line is frosted all the time, and occasionally I have observed the return line (about 20") also being frosted within the box.

Do these conditions indicate too much freon? Overall the total power consumption is about 175AH per day. This seems excessive to me as I believe that the refrigerator should be about 60AH. I would expect that the freezer would draw more but how much more? The refrigerator is about 7.25 cu ft and the freezer is 3.5 cu ft with 3" walls. Last night I turned the thermostat to zero and the freezer shut off. I then put it back to 3.5 and left it overnight. This morning the freezer had warmed to 24˚F from 11˚F last night (over 9 hours) and the freezer compressor wasn't running. I tapped the thermostat and a few minutes later the freezer compressor began to run.

Is it possible that the thermostat is "sticky" and is just causing the freezer to run excessively? I am not familiar with thermostat failure modes.

Answer: As long as Danfoss BD compressor runs and there is cooling you should not adjust refrigerant volume based on amperage. Tampering with refrigerant is destructive testing in most cases. Your unit has a capillary tube expansion device so correct refrigerant volume is always determined by temperature of ambient air cooling medium passing through condenser and frost area coverage on evaporator. In cool weather there will be slightly less evaporator surface area frosted and in hot weather there will be slight more cooling of line outside of refrigerator. When you have a thin plate evaporator with correct refrigerant charge and proper condenser cooling evaporator’s frosted area will be 90% to 100% covered and no frost on return line outside of refrigerated area.

On this unit the thermostat is a switch controlling the evaporator’s temperature.  Its calibration depends on where and how its sense tube is contacting evaporator. When correctly installed, the  thermostat will produce an evaporator temperature of about +12˚F with control knob set between 3 and 4. Box temperature will be relative to box design and present heat load.

It is possible for thermostat to freeze up and keep compressor running continuously if it is mounted too close to evaporator plate. Spray inside of thermostat switch with WD40 and work knob through off position several times. If problem reoccurs and thermostat if high in box away from evaporator replace it.

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11. Performance reporting Details


It would be helpful to know where folks are cruising when they make performance and amp hour consumption comments. Obviously one cruising in higher latitudes will have an easier time than someone close to the equator. These ambient air and sea temps have a huge impact on system performance. I found with my new to me boat that the refrigeration worked fine in New England when I bought the boat but after sailing home to Annapolis the unit was over charged with refrigerant for the warmer air and water temps. A careful bleed off of the excess under the direction of the esteemed R. Kollmann did the trick and the unit works well again.

Answer:  The comment on reporting a mobile refrigeration’s daily performance is correct. This energy information is of no value without knowing all operating conditions. Listed below are variable conditions I need to know when evaluating a reported refrigerator’s performance or energy usage:


1. Size of refrigerator box or boxes in cubic ft.

2. Controlled temperature in each box. Where in box was temperature recorded?

3. Manufacturer of refrigeration unit and compressor size.

4. Evaporator or plate manufacturer with model number and size.

5. Describe in detail where frost exists on evaporator. Frost should cover 90% of the evaporator’s surface area. Is there Frost on refrigerant line outside refrigerator,    if so how far does it extend on line toward compressor.

6. After refrigeration has run for several hours and box is cold Record and report            one complete cycle with thermostat set to 3 or 4. Cycle time starts when        compressor starts running till the next time it starts up again. Record both running   and off time. Example, compressor started 8:00 it stopped at 8:18 and restarted at         8:27

7. If the unit has a variable speed compressor what speed was it running at?

8. What is current draw (amperage) after compressor has run for more than 10    minutes?

9. Describe compressor condensing unit installation and how temperature of       condenser cooling medium is controlled during this performance test.

10. Refrigeration units are designed for maximum performance with standard day          70˚ F temperatures.. If condensing unit is air cooled what was average air temp         interring condenser? If water cooled what was approx raw water temperature?

11. Latitude location and date when daily energy readings were recorded.

12. Approximate amount of insulation and type.

13. What is temperature of insulation’s exterior surface? Does condensation ever            form on box’s exterior?

14. Was box kept closed on the day performance was recorded?


There are reports on the web where a four cubic ft refrigerator in one case consumed 18 amp-hrs per day and another four cubic refrigerator consumed 90 amp-hrs. Without knowledge of several of the above variables that legitimately determine daily power consumption these figures are of no value.

Changes in condenser cooling medium’s temperature will change balance of refrigerant pressures and refrigerant flow partially on systems with small condensing units. Manufacturers of these small Danfoss BD compressor systems have done their best to set refrigerant levels correctly for cruising climate conditions. It is better to adjust condenser cooling medium’s temperature than tampering with refrigerant to achieve best performance.

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12. BD50 with poor performance.


Thank you for maintaining such an informative web site. I have purchased both of your books and tried to troubleshoot my system but have questions.

The system is an AB/Waeco Cold Machine. It is a split system with a freezer having a pass through to the refrigerator with a thermostatically controlled fan. Model CU 101, BD 50 compressor, 134a refrigerant, manufactured October ’04. It is on a Beneteau 473; I believe Waeco manufactures a custom U shaped evaporator for Beneteau. It is about 480 sq.inches in area and is labeled Waeco/AB 55662. The refrigerator stat was turned off for this test so no air was being blown into the refrigerator. The freezer and refrigerator were empty. The stat in the freezer is a C1712JR680. The sensing tube has 5” in contact with the evaporator and does not contact the evaporator elsewhere. The stat was set at 3 ½ to start the test. The condenser coil is clean; the fan has been turned to blow out, away from the compressor. The exhaust air is ducted about two feet to an open area; the condenser has access to an unlimited volume of air. The test was done February 17th, in Jupiter, FL.

The LED indicator light did not flash at any time. The compressor ran continuously during the entire test.  I tested for leaks and could find none, however the joint where the copper tubes join the white tube is not accessible. The return line did have condensation, but not frost, on it at the condenser unit.

I have owned the boat for the last three years and have no knowledge of any previous service work. Since I purchased the boat, the compressor has run continuously when turned on. I started out thinking it may be a bad stat, but that does not appear to be the case now that I have gotten to testing it, as the freezer doesn’t seem to get down to temperature.

The amps shown on the attached table include the fan as it was measured at the service cable to the unit. One temp probe was located adjacent to the stat, one was in contact with the evaporator at the sensing tube. I’m confused…from my reading, high amperage draw seems to indicate an overfill situation. Condensation on the return line at the condenser may indicate an overfill. Maybe it was serviced prior to my purchasing it?


Each time I turn computer on I read your spread sheet and email and can’t think of an answer. The thermostat number ending in R680 indicates R refrigerator evaporator not F freezer thermostat. The 680 indicates a 680 ohm resistor is installed in thermostat wire to set compressor speed at 3000 rpm. If compressor never stops we can rule out thermostat, electronic control module and boat’s electrical wiring power supply.

Looking at 12 hour spread sheet compressor run:

Amperage draw over 12 hours of 6.8 high and 6.6 would indicate there is enough Btu energy being removed by 3000 rpm BD50 compressor or condenser cooling is inadequate and liquid refrigerant line is still hot after filter. Liquid line temperature leaving filter should be no warmer than 115˚F.

When the compressor runs continuously for 12 hours drawing 6 amps I would suspect evaporator temperature to be near zero degrees F. If compressor was cycling off and on with a refrigerator evaporator thermostat set at mid range then 13º to 17º evaporator temperature would be correct and insufficient to keep spillover refrigerator section cold enough.

With 100% of the evaporator’s surface area frost covered and no frost on refrigerant return line, it doesn’t sound like a refrigerant problem.

I do not know the box size or if insulation contains moisture but with ambient air in the 70’s I still think evaporator temp and amperage should be lower after running 12 hours with compressor running continuous.

Your report is one of the best I have gotten and the only recommendation I have is to confirm compressor never stops by removing wires from thermostat and connecting then together, Eliminating thermostat while keeping compressor speed at 3000  rpm. If problem is elsewhere it must be because box’s daily heat load is too large for a BD50 condensing unit.

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13. Cool Blue performance


Hi there, I hope you can help. I've got a problem with my Cool Blue. (BD35F and extra large 2.5 inch holding plate)  I had to remove the holding plate to add an extra 3 inches of insulation in the freezer box. Unfortunately I broke an o ring and lost the gas when putting the plate back on.

The leak has now been fixed and gas is staying in (it was vacuumed down). However my fridge engineer is unsure how much R134a to put in. Can anyone help? What weight of gas, and also what pressure should there be on the gauges?

Secondly, we've put some gas in and currently the compressor cools down the box to approx 10-14˚F before 'heating up' the box to about 35˚F and then cooling down again with the compressor running constantly. As a guess I think the expansion valve is freezing up? Would this be because of too much gas, too little gas or do I still have moisture in the system? As a reference the box would cool to about -2˚F with the compressor running constantly before we added the extra insulation.

Answer: It does sound like there is moisture in system. A quick check for moisture in TXV is, when it warms up, place a hot wet rag on the valve. Heat will melt ice in the valve allowing ice to melt and refrigerant to flow. A damp rag will freeze to valve temporarily until moisture freezes again blocking valve and then rag will fall free. See dehydration with vacuum pumps in Servicing Small Units.

 Because the Cool Blue has a liquid receiver and thermo expansion valve refrigerant charge is not as critical as a capillary tube system. I normally recommend adding enough refrigerant to obtain 6 to 8 psi of suction pressure when complete system is warm. This, over time, will slowly freeze plate. Use the sight glass on top of receiver when plate is frozen solid, add more refrigerant, if necessary, till sight glass bubbles are so small they look like white foam then add a little more refrigerant till sight glass almost clears to all liquid. When adding refrigerant, do it in short bursts and wait for system to stabilize before adding more refrigerant. This may take 5 minutes after each burst of refrigerant. Too much refrigerant will increase daily energy used.

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14. AB Poor performance Will not Shut Off

Several weeks ago, I defrosted the freezer and when I re-energized the circuit, the compressor ran for a whole day. I called an HVAC tech who tested the system and showed me that it had 6 p.s.i. of refrigerant. He increased that to 11 p.s.i. and the system still would not shut off. I cycled the freezer manually, believing that the problem was with the thermostat. Since I am in the Bahamas, parts are not easy to come by so I continued cycling the system on and off manually.

After several days, the freezer shut off by itself and I believed I was home free.
Not so......a couple of weeks later, it happened again. I lowered the thermostat to the #1 setting and it continued to run. After several hours, I started to cycle the system manually again. After a couple of days, the system started to cycle on and off by itself again and I continually lowered the thermostat to a setting of #5 where it is maintaining 20˚F.
At no time was there frost on the lines at the compressor and the evaporator was functioning properly.

What can be the problem? My guess is the thermostat but it seems to work more often than not.

Answer: What Make refrigeration unit do you have? Is system a Frigoboat keel cooler type? If condenser is air cooled, is there adequate air passing through it? Is it free of dirt and dust blockage? Is system 12 volt? Can you determine how much current unit is drawing after running for more than 20 minutes? If evaporator is aluminum and unit is serviced correctly with refrigerant, there should be frost covering 90% of evaporator's surface area. Describe area of frost? Thermostat can be easily tested but I need to know the type system you have.


The system is an Adler Barbour and is six years old. It is air cooled. Two months ago, before the problems started, I cleaned the supply tube and condenser coil to ensure an unrestricted flow of air. The current draw is approximately 4.5 amps and it is a 12 volt system. 100% of the evaporator is covered with frost.

Answer:  A Six year old Adler Barbour would indicate it has a BD50 variable speed Compressor. There were four optional evaporators for that unit, a stainless steel Power Plate for small icebox conversions, a 10 X11X6 inch bin, a 15X12X6 inch bin and a large thin plate that could be bent to fit a box. When these evaporators were sold each came with a thermostat and predetermined compressor speed control resistor installed in wire one to two inches from thermostat. Evaporators for small boxes require low compressor speeds to be energy efficient and larger evaporators came with larger resistors to increase compressor speed matching Btu capacity of evaporator. Slow compressor speed has a better coefficient of energy performance than running compressor at high speed. The BD50 with no speed resistor in thermostat wire will run at slow speed of 2000 rpm, with a 1500 ohm resistor compressor will run at max speed of 3500 rpm.

Defrosting a refrigerator in a warm climate causes high refrigerant pressure, which can expose the evaporator to pressures of over 80 psi. This high a pressure can cause micro size holes in an already oxidized evaporator

You reported 6 psi, on I assume suction side of system, with compressor running before tech tampered with refrigerant, if there was frost covering 100% of evaporator’s surface this would indicate maybe enough or too much refrigerant depending on high pressure/temperature. If evaporator were frosted, raising suction pressure from 6 to 11 psi may be too high if condenser air cooling is adequate.

Amperage reported of 4.5 amps would indicate compressor is running under a light load caused by speed too slow, or system leak due to low refrigerant. Normal load of 4 to 6.5 amps would be expected depending on compressor speed and evaporator temperature.


1. This compressor running at 4.5 amps continuously and full evaporator frost    cover should drop evaporator to a temperature below zero degree F. This assumes         there is no frost on refrigerant line outside refrigerator towards compressor.

2. To by pass and eliminate thermostat as cause for poor performance place a      jumper wire across terminals on back of thermostat. The longer compressor runs            the lower box temperature. Example: evaporator will drop to below zero in 12     hours.

3. To rule out refrigerant leak recheck frost coverage on evaporator’s surface.

What was done to this unit from the time system performed well and it first started giving trouble? Did anyone tamper with it or its thermostat? What was the normal thermostat setting? A setting of 3 to 4 generally produces evaporator temperatures of +12 degrees F. 

Reply: The unit has a large thin plate that has been bent to fit the inside of the box with one inch stand offs. The system has always performed continuously, but never well. It never achieved a temp of 12˚F at a setting of 3 or 4. To get the system down to 10 degrees or less, the thermostat setting had to be 6 to 7. We have never been able to freeze ice cream. For the past three years, the setting has always been the same 6.5.

 The entire evaporator is covered with ice at this time and the system is operating properly. It is currently set on 6 and the temperature is 12˚F. The immediate current draw is 5 amps. The refrigerant lines are in a wall and are not visible except for the last 3 feet at the compressor end. The total length of the lines I would guess to be approximately 5 feet. Therefore, I am unable to see the first two feet of the line but there is no frost on the lines that I can see, nor is there any water accumulation indicating that there had been frost that melted previously.

Answer: An Adler Barbour with BD50 compressor averaging 5 amps with good condenser cooling indicates your system will be producing adequate cooling. If compressor under these conditions runs more than 50% of the time thermostat is not cause of poor performance. Bypassing thermostat as I recommended will confirm thermostat is not cause of problem. If refrigeration unit is performing correctly then heat load of refrigerator box has to be evaluated. If compressor does cycle off running less than 50% of the time with a thermostat setting of 7 then it can be recalibrated to 3 or 4 permitting colder settings if needed.

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15. New Isotherm Performance


Mr. Kollmann: I have your book and appreciate the service you provide to mariners on refrigeration. I have just installed a new Isotherm 2554 SP unit in my 12 year old Beneteau. (I realize that you are not keen on the Isotherm, but it was a deal). I plan to use it in a spillover configuration. The installation went smoothly - following all instructions and diagrams carefully - and I am now running some tests, and right off, I notice some unusual events after running for 24 hours:
1. The refrigerator box has only reached 47˚F. (about 6 cu. ft. - will         eventually divide 1/3 - 2/3 freezer to refer)
2. The BD 50 is VERY hot – 125˚F tested with an infra-red thermometer.
3. The capillary tube on the evaporator registers about +3 to +4˚F - I would expect         this to be much colder for a freezer (I did purchase Isotherm's optional thermostat     with resistor).
4. I tested the voltage at the Danfoss connections: 12.25 volts. It is consistently drawing 3.0 amps (seems low, yes?)
5. The original issue Frigoboat unit (MUCH smaller capacity) used to freeze       water for ice, so I know the box is capable of delivering the required performance - I upgraded to the Isotherm to achieve even better performance. The Frigoboat         unit still functions and remains as backup/additional capacity in the tropics,            should I ever get there. I currently live in South Carolina on a tidal creek - current     water temp: 73.9˚. F.

Any suggestions? I'm thinking maybe the R134a charge is low? Where can I purchase the proper hoses to recharge with auto store R134a refrigerant, I wonder?

Answer: As I understand it your Isotherm 2554 has a through hull condenser with BD50 compressor and their standard flat aluminum plate evaporator 12 00 mm length by 190 mm high

Unit is drawing 3 amps and seawater is 74˚. After running several hours describe how much of evaporator’s surface area is covered with frost. Is there frost on line outside refrigerator on line returning to compressor?

Need this information:

Isotherm may be using one of their add on control boxes green, orange or another color attached to Danfoss black control module, if your unit has only the Original Danfoss module

Turn off circuit breaker to unit.

Then disconnect thermostat wires from module terminals C and T. Question, is there a resistor in series with one of these wires?

Place a jumper wire between C and T module terminals.

Turn unit’s circuit breaker on and let it run continuously for at least 12 hours.

Now with an ohmmeter check resistance between the two wires you removed from module terminals C and T to get continuity through thermostat it must be set to a cold setting. Resistance will be zero or anything up to 1500 ohms if there is a speed resistor in wiring. Record reading.

Another test after unit has run for more than one hour, Feel the two lines coming out of compressor. The high pressure line will be to hot to hold fingers on. Report temp condition of each line. Next go to the two lines several inches from condenser through hull and feel temperature of each. The line to condenser will be hot the return line after being cooled by seawater will be only slightly warm and comfortable enough to keep the back of your hand’s soft skin on it.

I have never used these temp guns to red ¼ line temperatures so after recording the hand touch tests see what the gun readings will show.

I am concerned about your voltage reading of 12.25 volts. The Danfoss module may see a start up voltage spike below that and prevent compressor from running. On these new modules the fan may continue to run when compressor stops due to low voltage and you may think you have a performance problem when it’s a boat electrical problem. Input battery voltage must always be above 12.5 volts to handle low voltage spike on start up.

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16. BD Thermostat performance


Richard - an update. We’ve-measured our box and discovered it was in fact 147 litres and not 117 litres so we bit the bullet bought and installed the 160H freezer evaporator. Frigoboat recommend running the speed control at 2500rpm which we are doing. The plate is freezing lightly at setting 5.5. The fridge itself appears colder than before and we are able to freeze meat in the freezer compartment. We have also put more bottles of water in the fridge. However the compressor still appears to run fairly regularly. It cranks in about 6 amps and reduces to about 4.7 amps. I have noted the comments on your web site Re. the position of the sensor of the thermostat. Frigoboats literature is pretty specific about how much should poke out etc - but I can play with this. In the mean time thanks for your help.

Answer:  Numbers on thermostats are only for reference. If desired box temperatures can be maintained at a thermostat setting of 5.5 do not mess with thermostat. Your thermostat controls evaporator temperature and evaporator’s rate of heat transfer controls box temperature. If BD 35 compressor is drawing 4.7 amps when in normal stable operation and running 50% of the time or less during stable operation the system is performing correctly.

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17. New Adler Barbour Problems


System is less than a year old. Worked great when installed and ran fine for 8 months in the tropics. CU200 (water cooling NOT connected) and large V160 evaporator plate. About 7 months after installation the box temp started to go up. We noticed ice build up on the evaporator so we defrosted the system by turning it off and melting the ice with a hair dryer. While defrosting ,the thermostat was not adjusted. After defrosting the box temp did not get cold enough so we adjusted the thermostat to it's lowest setting and the box got cold again and cycled on and off normally. But we don't know why we had to adjust the thermostat to get it cold enough. None the less it seemed ok for a few weeks after that. Then a month later (3 days ago) the box temp started to go up again. We noticed ice around the little plate where the thermostat tube is attached to the evaporator plate so we defrosted again. Now the box will not get cold like it used to, and the fridge has run continuously for 3 days.

We cleaned the condenser, and made sure that the thermostat sensor tube isn't touching the evaporator plate. Battery voltage is good. Thermostat is set to as low as it can go. The compressor hasn't shut off in three days. The system current draw is about 6 amps when first started and drops to around 4.5 or 5 amps after running for a while. Evaporator plate is covered with frost.

Answer: I can only guess why after defrosting you experienced a change in cooling probably oil trapped in low tube area of power plate.

Your compressor is set to run at either 2500 or 3000 rpm because the power plate evaporator is designed for small boxes 4.5 to 5 amps confirms this. At 5 amps and if compressor is running all the time every thing in box should be frozen. If you are saying when thermostat is set to number one on the dial (warmest setting), box is too cold and compressor never stops, then thermostat or its wiring is the cause. Does compressor stop when thermostat is turned to off position? 

Reply: I apologize....the evaporator plate is a VD-153, it's not a powerplate. I misread the pat number. The resistor in line with the thermostat is the one that was installed by Adler Barbour and shipped with the evaporator plate. I therefore assume that it's the right value for the VD-153 evaporator plate.

Compressor stops running when thermostat is turned up (warmer - to 1).When the system was first installed the thermostat was set to about 4 and the box got quite cold.

After defrosting a month ago, the compressor shut off when the box temperature was not cold enough (not as cold as before I defrosted) even though the thermostat had not been touched. So I then adjusted the thermostat to the coldest setting. The fridge got colder and the compressor shut off with a similar duty cycle to when it was originally installed. But I had no explanation for needing to adjust the thermostat like that. The only thing that I did was defrost it. Everything seemed ok except that I found it necessary to set the thermostat to 7 to get the box cold enough and to get the system to cycle on and off.

The thermostat is still set to 7 and since I defrosted again 3 days ago the box gets cold, but not as cold as it did and the compressor now never shuts off. Bottom line - It seems that the inside of the box is running about 10˚F warmer than it was before I defrosted it for the second time, even with the thermostat turned all the way up to 7. And the compressor hasn't shut off in 3 days. I'm sure I could adjust the thermostat to allow the system to cycle on and off, but the problem is that it doesn't get as cold as it did before I defrosted it. Could the system have been damaged by my using a hair dryer to defrost it more quickly?

Answer: Good that you do not have power plate. Performance of standard evaporators is much easier to identify from amperage and areas covered by frost.  Amperage tells us how much work is delivered by compressor to refrigerant flow control device. If saturated liquid refrigerant pressure is not too warm or too cold refrigerant will absorb heat over 100% of evaporator’s surface area and not have frost return line outside refrigerator back towards compressor.

1. Amperage reported 4.5 to 5 is normal for BD50 compressor at mid speed range.

2. Liquid temperature after condenser of line to evaporator should be 90 to 115˚F,          not hot. If this line is hot condenser coil airflow is restricted, is this area. Is it           dirty or is airflow blocked?

3. Is there frost covering 100% of evaporator’s surface?

Thermostat Operation: Adler Barbour’s standard thermostat has a long thin temperature sense tube on BD 50 units and the end of this tube has a thin plastic tube cover. The last five inches of sense tube is bent into a U shape and sandwich clamped with a plate to evaporator? With only five inches of insulated sense tube contacting evaporator its plate temperature will be around +12˚ with thermostat knob set in position 3 or 4. If your thermostat knob must be set on 10 the coldest refrigerator setting and items 1, 2, and 3 are correct maybe not enough sense tube is clamped snugly against evaporator.

Compressor duty cycle running of 50% or less is desirable on variable speed compressors like yours. The run time you report is 2 to 3 times greater than expected. You reported:

·          Line from condenser to evaporator plate is around 105˚F.

·          Frost covers 100% of the evaporator plate.

·          The system current draw is about 6 amps when first started and drops to around 4.5 or 5      amps after running for a while.

 Each of the items reported with the exception of compressor running time would say refrigeration system is performing correctly.  This then does not explain change you believe occurred.  he information so far seems to indicate an increase in box’s heat load rather than a refrigeration problem. At this point I suggest increasing compressor output by increasing resistor size in thermostat wire. The large evaporator you have can handle compressor output at 3000 or 3500 rpm. After removing inline resistor from thermostat wire a 700 ohm resistor can be installed to produce 3000 rpm or a 1500 ohm resistor will produce 3500 rpm. Daily energy consumption is best if compressor can run at its slowest speed and runs less than 50% of the time while keeping box temperature at desired temperature.

Reply: I can do that. In fact, I had a thought and would like to run it by you and see what you think. I was thinking of building a small circuit with resistors and a switch so that I can change compressor speed and find the speed that gives best performance. Living "on the hook" makes optimal performance pretty important to me.

On that note: Can you please clarify what speed changes do for the system performance wise? Is a faster compressor speed better for the tropics while a slower speed is better for more temperate climates (or vice versa)? I assume that a faster compressor speed will draw more power which might be offset by a reduced duty cycle? Is that the idea? If you have time, I'd like to learn more.

Answer: You first need to determine what speed compressor is running at either by measuring thermostat resistance or replacing resistor. We know you believe compressor is running too long but have not confirmed that by running compressor continually for 12 hours. The only way to compare daily performance is by  recording amp-hrs consumed when box is stable at desired operating temperature for twenty four hours. 

As far as understanding Variable speed compressors what I said before is the simplest way to explain them, “Daily energy consumption is best if compressor can run at its slowest speed and runs less than 50% of the time while keeping box temperature at desired temperature.”

Pleasure boat iceboxes converted to 12 volt refrigerators were not efficient in the past because, in most cases, conversion kits rarely were compatible with a particular size boxed or temperature conditions. Twenty years ago most companies like Adler Barbour sold 12 volt one size fits all icebox conversion units. Adler Barbour’s unit was designed to supply 300 btu of cooling to evaporator when evaporator temperature was maintained +12!F. If this fixed speed AB unit were installed in a 4 cu ft icebox insulated to an R value of 30, exposed to an ambient air temp of 70˚ it would cycle too often overpowering the evaporator and wasting energy with each start cycle. If Btu capacity of compressor could be reduced and still maintain box temperature ,there would be a reduction in energy used. The problem with reduced compressor speed is at some point the compressor by running longer will use more energy. Switching speed resistors is a good method for seasonal weather changes but if a boater wants automatic speed adjustments daily Danfoss Adaptive Energy Optimization (AEO) Module is the best next best thing is Frigoboat’s Smart Speed Control.


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18. Tropics versus Cold Climate refrigerant performance.


I've read through your books twice now  I have a pretty good picture of
what direction I need to head. The one topic that confuses me is cold water
application. Say we design, build, tune and test a refrigerator for
tropical conditions, then decide to head to Maine. The picture I get from
your readings is that we need to reduce the capacity of the condenser by
disabling a fan or throttling back seawater flow. Wouldn't the unit just
run less and be more efficient in cooler climate without doing this? If I
can make a unit 50% duty cycle in the Bahamas, then would it run, say 30%
(less energy) in Maine.

In other words, there must be a parameter that we are trying to manage. I
know we need to superheat on the evaporator and subcool on the condenser.
In a cooler climate where we drop the subcool temp, the TEV would just shut
off earlier without liquid flow to the compressor? I think I'm barking up
the right tree when taking about phase change, but I can't wrap my head
around why.

Answer: When considering mobile refrigeration design on a pleasure boat there are 3 different types and sizes of units, ¾ HP and larger engine drive compressor condenser systems, ¼ HP 110 volt AC and 12/24 volt large DC units and 1/20 HP and even smaller 12 volt systems. Each of these systems use vapor compression to cause gas to change to a liquid and then boil it off in the evaporator’s very low pressure absorbing heat by flash evaporation.

Each of the above systems must have a refrigerant flow control device to separate high pressure saturated liquid from low pressure in the evaporator. In large pleasure boat refrigeration systems greater than 1/6 HP a Thermo Expansion Valves along with liquid receivers provides a far greater evaporator Superheat control than the less expensive capillary tube expansion devices used on small 12 volt systems.

No matter what size refrigeration system you have the compressor must be capable of delivering high pressure through condenser to expansion valve. Condenser needs to remove process heat and still maintain enough heat to insure pressure for expansion device to deliver correct range of pressure differences between high and low sides of system.

To answer the question about refrigerator performance changes from warm to cold climates or the reverse I will stay with a small 12 volt unit design similar to an Adler Barbour to be used in mobile environments like boats. The design engineer selects a compressor, its speed set to match evaporator’s capacity, and then a condenser capable of handling compressors planned output. Unless this system is designed for a special application the condenser will probably be designed for a standard day cooling medium temperature of 70˚F. This design based on standard day temp of 70˚F will reduce or increase the efficiency of refrigerant flow affecting total system performance. On a Capillary tube system refrigerant volume is critical. One ounce too much or too short will result in very poor performance. Major changes in cooling medium’s temperature on a capillary tube system will change refrigerant required charge. Chances are if a unit still has the factory refrigerant charge and no one has tampered with it the boat captain will not see much of a change with a correctly installed air cooled condensing unit. Adler Barbour posted instruction years ago when operating in cold climates to block off part of the condenser reducing airflow and increasing saturated liquid pressure. Unlike large refrigeration systems where high refrigerant pressure can be controlled by controlling cooling medium flow. The solution for small 12 volt systems is to in stall an air cooled condensing unit inside the boat where air is more moderate and stable whereever you cruise.

It is a fact that if condenser cooling can not be maintained within an expectable pressure temperature range on a capillary tube system evaporator superheat will be out of control and so will system’s performance. 

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19. Poor Performance Frigoboat


I can't tell you how much you are appreciated - but sad to say I still have a mess. I have purchased your book but have lent it to the person who is working up the gauge set for measuring what is in my system after one Canadian boat yard and two Canadian HVAC professionals mucked around in it (see below). By the way, there is just no one in the Chicago area who claims any real knowledge of 12v refrigeration! A couple claim they know Air Conditioning but refuse to touch refrigeration!

My installation - Vecco (Frigoboat) stainless box with built in evaporator has high and low tubes going through woodwork until their full length ends under the kitchen sink cabinet floor board. Then there is a coupling and coiled tubes which then go to the boat’s engine room and have another coupler just inches from the compressor. So the overall length of the tubes is a bit upwards of ten feet. I am told the compressor is a BD 2.5 by Vecco running on R 134A. The compressor says fill is 0.100 KG .The control board is the 102N3030. It is a water cooled unit with a Flojet pump - the water has its own intake but dumps into a standpipe shared by two sinks. The unit functioned quietly for years - but always drew a lot of current - up at 6-7 amps. I am told the box is 130liters.

Two years ago - when in Canada - and the boat was being stored in Canada that season - I noticed that the compressor was running hot and the water pump was not running. The box was not quite cold enough. I told the Canadian yard to please repair it - and gave them the boat end of August. I don't know what they did or when they did it. I do know in the following June before I got the boat (it was not ready they said) they ordered a new Flojet pump - and then worked on the system.

When I got possession of the boat in July the water pump was causing the standpipe to back up into and overflow the sinks if anything was being done in the sinks while the fridge ran. The compressor ran almost all the time and the electric consumption was horrific. In addition it was very noisy - I think it was just the water pump making noise. I called about this and was told they were sent a funky pump and that it should be replaced with a new one when they would get it, they did not know.

I then probably made matters worse. I called in another port an HVAC person - who came out and found that 1 ) the Canadian distributor knew nothing about service parameters and 2) the USA distributor did not have a table of operational pressures from which the HVAC person could troubleshoot. So he barreled ahead and evacuated and recharged. oh oh.

Later I found that the coupling just before the compressor was frosting - and that that was too close to the compressor. Another HVAC person came and recharged to no avail and then with some help from frigoboat released some of the gas to the point that the coupler under the sink stopped frosting. There was no way to get to the tubes near the evaporator.

The boat went in storage. The Canadian distributor provided a new water pump which was installed exactly as the other - including wiring connectors. (but this was of course after the first yard worked on the unit).

After launch the refrigerator did not work. The evaporator plate (rather the stainless wall over the plate) sweats inside the box, even the compressor's bottom gets cold enough to sweat (and this never happened before).

I believe that the system was overcharged - maybe it still is. I have disconnected the thermostat and jumped the connection - no change. I have also disconnected the pump (positive side only) it stopped but I now realize you have instructions to remove the negative side connection only.

Need I do that? One of the problems with pressure measurements is that the high and low side couplers are the same as low side R12 couplers, so the HVAC standard gauge bridge cannot be properly attached. I am having a custom gauge made for the high side so that the bridge can be properly used.

So I am left with - what are the guidelines for the HVAC person to work the pressures to correct? Could the compressor be damaged? Or could this just be the controller? Don't I have to get the pressures correct even if I have to replace the compressor - because it comes precharged and if the evaporator and tubes are properly charged it is then a mundane connection.

Anything I should do before doing the pressure? Would an LED between the C+ and the D on the controller give me any information? If so what voltage should it be?

Answer:  Module picture confirms your unit is either a BD 2.5 or a BD3 fixed speed compressor. The label on compressor says 134a refrigerant so compressor must be a BD3 model.

To determine performance You can use visual indications of frosted areas during a test. Amperage readings during test will help if you have a way to read digital amps from 4 to 7 amps. Suction gauge reading are risky so I prefer not to have inexperienced people connect gauges to this small system. Most experienced technicians would also not want to connect high pressure gauge to a unit that holds less than 5 ounces of refrigerant. The only part of your system I have no picture of is the evaporator, is it the standard thin plate aluminum or a copper coil covered with a stainless steel pan.

To run this test for me water pump must run whenever the compressor runs. Leave jumper wire on thermostat connections. Turn off unit for one hour or more before starting test. Evaporator must be well above freezing temperatures.

1. Record this information every 10 minutes for one hour:

2. Amperage if you have a way to read it.

3. Describe in detail frost coverage on evaporator’s surface It will be anywhere    from condensation to zero frost or 5% of area frosted to 100 % of area frosted.

4. Is there frost on return line headed back to compressor? If so how many inches          is line frosted?

5. Is there any frost on any other place on system? If so describe part.

6. What are line temperatures report as hot warm cool or cold.

           a.Line from compressor to water condenser?

           b. Line from condenser towards evaporator?

           c. Line return line to compressor?

Compressor temperature. One reading only of: approximant cabin air temp and seawater temperature.

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20. Adler Barbour Power plate Performance


I have spent much time this summer observing and making small changes to refrigerant levels, etc.

I have concluded that the VD-160 is not functioning, either because it is defective and not full of solution, or perhaps because of a kink in the tubing during installation which I cannot see or some other restriction. So I plan to remove the Power Plate and replace it with an open aluminum evaporator.

My assumption is that the small vertical evaporator is the best match. - It is for up to 9 cubic feet and my box is 5.

Is there any advantage or disadvantage to getting the larger vertical evaporator instead? I understand that it would provide a slightly larger freezer compartment, but after initial cool down would the power consumption or cycling pattern be different?

Answer: Adler Barbour cold machines with their small chamber evaporator, when used in a five cu ft box, is a good match. Based on your reported frost pattern and if amperage is under 6 amps I still suspect contaminated refrigerant. And do not recommend changing evaporator. If you do replace power plate be sure you dehydrate system completely and use the correct refrigerant for that model compressor.


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21. Old AB Question performance.


Many problems, but, we reconnected the small evaporator cold box to the side of the insulated compartment (where it had been bolted before but taken off by persons unknown), we turned on the compressor which is wired into the power panel, and it runs. We are using shore power and the built in battery charger while it’s docked. It’s cooling a bit but we don’t know all the particulars about adequate batteries, efficiency, etc.

Don’t want to blow out our batteries they are already a couple years old. (Slow going) I left the unit on to see if it would make ice cubes in the two trays that came with the small 6x11x evaporator /analog switch.) Unfortunately, we had to leave the boat for a few days and I forgot to turn it off. Hopefully it didn’t burn up or burn out our batteries or charger. My husband said we can use an ice chest cooler and suggested we throw out the unit like he did the macerator, air conditioner, and the entire electrical system. He had a marine electrician rewire the boat (including to the Danfoss) with a larger inverter and a special voltage regulator but no power monitor other than the needle amp meters on the electrical panel to the two batteries. We are having power problems –the motor didn’t recharge the batteries underway so we motored overnight in the dark in the Gulf of Mexico. That’s another problem. 

My goal is to try and figure out this refrigerator and make it work. I will attempt to read your material and learn as best I can but I’m not too mechanical.

If we need parts or to test our 4 pin module, do you still do this? I tried to read the metal plate on the compressor which appears to read:


Adler Barbour Model DCM 12

Refrigerant RTZ  (?R17?) 3507

Serial E 11857

Circuit DC 12 volt ?5.4AMPS cut in 11.5VDC

factory test pressure high 250lbs

test pressure cut out 10.5VDC

on the top of the round compressor unit is stamped:


BD2 102Z3011

2.0 A30115A

N213EH (or 1)2N

12VV  DC

0 280 cm3 oi? a tear or scrape on rest

Adler Barbour Inc Systems Pelham NY 10803 USA

Do these numbers sound right?  It was hard to read the stamped old numbers/letters. There was no paperwork of course. The boat had 24 translucent frogs living on board when we got it.

We are going back to the boat on Monday, at Boca Chica Navy Marina near Key West. Have a refrigerator thermometer to put in box. Am optimistic. Again, thank you for your great site.

Answer:  Your Adler Barbour refrigeration unit is at least 25 years old but age is not a problem for this unit. You are fortunate that when reconnecting the evaporator lines there was still refrigerant sealed up in both sides of system. This system with a BD2 compressor will have Freon R12 refrigerant in it and will require only R12 if additional refrigerant is needed. 25 years ago the fan used for cooling was not efficient nor was it shrouded to insure positive airflow through condenser.

The Danfoss electronic module will prevent the refrigeration unit from destroying the battery by shutting the compressor down when battery voltage drops below 10.5 volts. Battery life will depend on you keeping them ALWAYS charged above 12.2 volts

It is a simple task for you to determine condition of this refrigeration unit:

To check refrigerant charge let unit run for several hours then visually check the evaporator for amount of frost cover. If frost appears to cover more than 80% of evaporators surface area then refrigerant volume and flow is OK.

BD2 Compressor’s are not life limited but evaporators are if exposed to internal or exterior corrosion. Evidence of evaporator corrosion shows up as exterior bubbles in paint coating or missing protecting paint spots.

If the cooling fan has an external motor and metal fan blade it should be replaced with a 4 inch muffin fan. To improvise a shroud to force fan air through condenser, stuff foam around open areas around muffin fan.

Watch the slide show on my web site at  for additional help.


22. WAECO BD return line condensate performance


My tubes are not icing up, there is just a lot of condensation dripping off of them. I was thinking that the additional insulation might help to prevent this.

Answer:  Condensation on refrigerant return line to compressor is not as bad as energy wasting frost on that line. Manufacturers that design for tropical climates, like where you are in the West Indies, install a section of tube insulation on return line outside refrigerator to improve performance and reduce unwanted condensation inside boat. They also run refrigerant flow control capillary tube inside and around return line several times to improve liquid refrigerant sub-cooling. To compensate for extreme warm climate conditions refrigerant lines are either clamped together or spot soldered together every two feet. With these two lines touching it allows heat to be absorbed by return line eliminating condensation. It is said that “Sub-cooling can have a dramatic effect on the capacity of a refrigeration system - as a general rule; a 1% increase in refrigeration capacity can be achieved for every 2 degrees of liquid sub-cooling”.

Tapping your lines together at a few spots and adding an additional 4 ft of tube insulation over bundled tubes should eliminate your condensation problems.
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