Too Much Refrigerant


  • Too Much Refrigerant in Small Capillary tube System
  • Common complaints, refrigeration technician added too much refrigerant. Poor performance and frost on refrigerant line returning to compressor


    Things to remember if refrigerant level is in question:
    • Do not connect gauges needlessly always perform non destructive testing first.
    • Purge gauge set.
    • The box and complete system must be warm when adjusting refrigerant charge.
    • Adjusting refrigerant charge when evaporator is cold may not produce good efficiency.
    • Don’t connect refrigerant gauges when compressor is running, it is a good way to contaminate refrigerant


    Action recommended:

           1. Stop compressor and remove a very, very small amount of refrigerant. Run system 15 minutes, then check frost line it should not extend on un-insulated line more than a few inches outside refrigerated box in cold weather, in warm weather only condensation should be present outside the box. If there is still too much frost stop compressor and repeat process. When operating properly there must be a layer of ice forming over 90% of evaporator’s surface. If too much refrigerant is removed there will be an area of the evaporator without frost.

          2.  Once the system is operating OK set the thermostat to full cold for at least 12 hours. If at the end of this test run evaporator has lost its frost and evaporator is cold with only condensation on it there is moisture in the refrigerant.

          3.  If letting out refrigerant did not solve the performance problem or system freezes up due to moisture, a refrigeration vacuum pump will be required to remove air, moisture or incorrect gases.


    I don’t like to connect gauges to a system until I have proven that the refrigerant is the problem. Make sure there is adequate airflow through the condenser. If your evaporator is a thin aluminum plate and not an Adler Barbour Power Plate the frost line will indicate if the refrigerant charge is correct. When there is sufficient refrigerant there will be frost covering 90% of the evaporator’s surface and no bare spots. One half an ounce too much refrigerant on a small cap tube system could double the daily amp-hrs consumed, see chart on page 56 in 12/24 volt book.

    You will find answers to your questions on connecting 134a refrigerant to standard gauge set on page 57 under Pre-servicing Information. Acme Fitting also pictured page 57 on compressor suction service port.


    Adler Barbour’s new super cold machine with BD 50 compressor has the same components as the cold machine except the super unit has a small supplemental water condenser on liquid pressure line. Servicing a DB50 with a capillary tube expansion device is the same as servicing your old BD compressor except with 134a there is a small pressure difference. If you do need to add refrigerant follow the steps listed on page 58 and 59 to the letter and you will end up with an efficient system.

    Twelve volt units with Too much refrigerants and finding leaks

    A frequent problem that occurs when servicing a 12/24 volt small refrigeration unit is that you or a service tech has added too much refrigerant to the system. While the unit is overcharged, check to see if there is frost on the return line and a 3 LED signal. This will confirm that too much refrigerant has been added. The first thing that you must do is to check for any leaks that might have been overlooked prior to servicing.


    First check for any leaks: The areas to check for leaks on AB Cold Machines are: mechanical line connections, the three refrigerant service connection leak proof caps and line connections at the power plate, if you have one, instead of a standard aluminum evaporator.

    By using a one inch paint brush and a 50/50 mixture of liquid soap and water you will be able to find leaks as small as a ½ ounce per six months if you follow these instructions:

    • With the complete system warm and turned off and the refrigerant overcharged there will be more than 50 psi in the complete system.
    • Apply the liquid mixture to one location at a time. Use brush tips to stab the fitting. This will break the surface tension. Continue stabbing on the mixture until a foam is generated that looks like shaving cream.
    • Watch that fitting for two to three minutes before moving to the next fitting.

    If one of the serving caps or line connectors are leaking, use two wrenches to tighten but never tighten any tighter than what it takes to stop the leak. Some of the power plates have O rings as seals so in order to stop a leak there, it may be necessary to remove the refrigerant and replace the O ring seal.


    To correct an overload - indicated by frost on the return line and confirmed by three LED flashes, do the following:

    • With the compressor stopped for at least 5 minutes, depress the servicing port, valve core located at the top of the compressor, NOT at the line service valves, for 3 seconds allowing the refrigerant to escape, then, replace the sealing cap over the valve.
    • Start the compressor, if the amperage drops quickly below 8 amps, the compressor should run. I have an Adler Barbour with a BD50 compressor on one of my test stand and AB’s small bin evaporator at a controlled temperature of 80 + 1˚F Start amperage after one minute is 6.5 amps. If your system’s evaporator is colder than 80˚, amperage may be less. If warmer than 80˚ the amperage may be slightly higher than 6.5 Amps.
    • If the compressor stops again because thr amperage is above 7.5 amps or you receive a 3 flash LED signal, repeat item 1. and 2, but this time release the gas for only 2 seconds. The compressor must be turned off for 5 minutes each time before releasing refrigerant and the leak proof cap must be installed tight when NOT releasing gas.
    • Repeat steps until the compressor runs without stopping even if amperage is still above 6.5 amps. Final fine tuning will depend on visual frost formation on the evaporator’s surface area and no frost on the return line and no amperage. as it will decrease as the plate temperature drops. There also may be an error in your amperage reading.


    After two or more hours running time the evaporator’s surface area should be covered 95 to 100% covered with a thin layer of frost with no frost on the return line outside of the refrigerated area on the line towards compressor.

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    3. Improperly serviced

    After 40 years in the tool and die business, I have switched professions to Marine canvas and Marine Refrigeration. Just today I was asked to charge an older AB system and found the compressor much warmer than I liked. I found the low side at 16 psi and compressor amperage at 7.6 equalized pressure on this system was 40 psi

    I bled the system down to 7-8 psi and normal ranges prevailed.

    My question may be more ethical than technical but this system was apparently charged by someone who didn't know where they were heading. Would it be prudent to advise the customer to pay for a recovery and deep vacuum with recharge to eliminate the possibility of air from lines they may not have bled properly . I don't know how many times they may have opened the system.

    Answer: I hear of at least two systems a week that have been serviced incorrectly. The first thing to determine is why it was necessary in the first place to tamper with refrigerant level. In many cases poor or no cooling performance relates an electrical problem with boat wiring or Danfoss compressor and not refrigerant volume. Once the decision is made to connect gauges to one of these small systems the door is open to major contamination problems. If refrigerant was truly needed then there is a leak and it needs to be found before evacuating and re-servicing. In the last twenty years I never charged for a service call to add refrigerant to one of these systems if I could not confirm and repair the leak.

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    4. Servicing BD (Variable speed compressor)Too much refrigerant ?


    This older unit is destined for service. It cools my 8cft freezer box, and I have installed a new CU-200 and vd -162 in the refrigerator portion- which is approximately 12-14 cuft with 4" insulation. For the fridge, I bought the evaporator new, but the compressor deck was 1 year old and had been used for that period. I removed the old couplings and soldered on new, also soldered on a new filter/dryer and then vacuumed the unit and charged it to the max it would hold with 134a. I then vacuumed it again and recharged to the max it would accept (65 psi) with 134a again. At that point I connected the unit to the evaporator per the instructions.
    Right now, at the coldest thermostat setting, (traditional non-digital thermostat) the unit cycles on for 5 minutes and off for 12. This keeps the box at or just under 40˚. I would prefer 35˚ or less. I wonder if I need to change the amount of refrigerant or adjust the thermostat. The compressor deck ambient temp is around 85˚ (inside the cabinet where it is installed).The total charge was around 58 psi in the compressor deck before I connected the evaporator. Please let me know the ideal run/rest times for the compressor and how much charge pressure should be in the system.


    Answer: If the AB compressor is less than five years old, it is most likely a BD50 compressor. Cycle time is not used to determine performance on these variable speed compressors. When you purchased the AB evaporator, it came with a thermostat and resistor that presets compressor speed to match Btu capacity of the evaporator. It sounds like you have overcharged the system with refrigerant by thinking static pressure is relative to correct refrigerant charge on this type system. When this system is correctly charged, there will be frost covering 95% of the evaporator and no frost outside of the box on return line. If refrigerant charge has the correct frost line, check the thermostat installation. The thermostat’s small capillary tube should only contact the evaporator under the clamp provided on the evaporator. AB recommends that a U shaped end be bent to 2 ½ in. This means 5 inches of tube is in contact with evaporator. The reason for having this amount of tube touching the evaporator is important as the thermostat control knob is placed in mid range so the operator can increase or lower temperatures from a normal setting of 3 to 4 on dial..


    5. Too much Refrigerant Now what do I Do?


    The unit I have is a cu-200 from 2006. It is a BD50. The thermostat capillary tube is correctly installed and the refrigerant tube frosts back about 5 feet. When it exits the box, there is no frost line, only inside the box.
    I am also quite positive I have overcharged the system, but I would like to know the correct operating pressures on suction and return, or just system pressure to get a ballpark figure on how much refrigerant this system needs. When the thermostat capillary tube was not installed on the evaporator the unit ran continuously with no faults indicated on the control unit led.

    Answer: Low and high pressures on a capillary tube system will vary depending on a number of factors, condenser cooling medium temperatures, heat load inside box, evaporator temperatures, quality of refrigerant and of course refrigerant volume. Typically with 134a refrigerant high pressure will be in a range of 115 to 125psi. Low pressure when beginning with a 70˚ F box and complete system at the same temperature will, after 10 minutes, stabilize between 6 and 8 psi, thereafter, suction pressure will decrease as evaporator temperature drops.

    Five ft of frost on the return line would indicate too much refrigerant on that manufacturer’s condensing unit and evaporator. Refrigerant volume is very critical on a refrigerator that incorporates a capillary tube expansion device and there is very little room for error if energy efficiency is important. To pre-charge your system, to a specific volume by weight is not possible for you to do. The only way to service your unit is by suction pressure, frost line or amperage. Assuming there are no restrictions in any connections you made in tubing (soldering small tubes together can cause blockage}, and refrigerant is 134a. Here is what to do to relieve the over-charged condition:

    1. With unit turned off, bleed off refrigerant for one second then wait five minutes and turn on power.
    2. Run unit long enough to form frost line and repeat the above process until frost line is retracted to within a few inches of evaporator. For pressures to equalize it is important to wait 5 minutes each time before starting compressor.
    3. Once overload condition is removed let unit run for one hour. Now check frost line on evaporator. With the correct refrigerant charge, the complete evaporator will have a thin layer of frost on 100% of its surface but no frost on line returning toward compressor.

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6. Servicing BD35 Another overcharged system


First, thanks for all your help and such a great web site. Both your books have been a great help.
I am trying to charge a new bd35 with an old box evaporator and oversized condenser per my last post. Ambient temperature is 80, pre-start pressure is 84psi, low motor speed.

After three minutes, I reach a low side pressure of 8, high side 110. Within 5 minutes, the low pressure moves back up to 15psi and stays there.

I get frost over the entire evaporator with an outside box temperature where the lines go in of 14 degrees.

Your book and prior posts suggest that I should get to 6-8 psi and then after the box cools, the pressure should continue to go down. My pressure drops to 8 then back to 15.
Any suggestions,
Thanks again for all of the valuable help.

Answer: The correct procedure was to start up a warm system and let it run 10 minutes then adjust 134a refrigerant suction pressure to 6 to 8 psi in the next five minutes. From then on pressure will drop as the evaporator cools and no more adjustments are made.

At 15 psi the evaporator will not get cold enough and power consumption will be twice normal. If you warm the system up, then reduce the suction pressure to 6-8, in a time window between 10 to 15 minutes the refrigerant level will be correct.

I would expect at 80˚ ambient and 2000 rpm the amp draw of a BD35 will be less than 3 amps.
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7. Return Line Icing Too Much Refrigerant

Why do I have frost on my refrigerant line all the way back to compressor?

Answer: Adler Barbour and other similar ice box conversion units supply a three foot piece of insulated tubing to use on the lines just outside the box. In moderate temperatures and humidity three feet of insulation should be enough to prevent moisture on the lines outside the box. There is one condition that will produce frosting on the return line and extend the compressor running time, and that is too much refrigerant in the system. The factory refrigerant charge will not cause this condition but if the system was field serviced with refrigerant that could cause the problem you describe.

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