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Cold AC compressor means what

Discussion in 'HVAC' started by CSkipR, Apr 25, 2017.

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  1. CSkipR

    CSkipR Member

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    I have two 16k R22 units. The top of one compressor runs approx. 100 degrees the other one about 55 degrees. Both are cooling but 55 degree compressor is not putting out as cold of air. Suction side read 55 and I charged it to 65. The compressor top heat was measured at 55 after charging it. What would a cold compressor top indicate if anything.
  2. Knight

    Knight Member

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    Air flow restrictions,, fan, overcharged, stuck open metering device or its freezing up. It sounds like your getting liquid refrigerant back to compressor.
  3. Capt Ralph

    Capt Ralph Senior Member

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    Overcharged R22.
    Are you suddenly an A/C Tech?
  4. CSkipR

    CSkipR Member

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    Not an ac tech just an owner that was taught how to flush & charge his units. Since marine ac companies are so busy its impossible to get them on relatively short notice. Yes I do try and learn everything I can about the boat so when I'm out of country I'm able to service if need be.
  5. wdrzal

    wdrzal Senior Member

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    It's Technically called "Heat of Compression" is why they get hot. About 7 to 15 percent of the heat of compression is rejected through the compressor shell with the rest rejected out the condenser. A cold compressor indicates one of the following: low charge (leak , no gas to compress), low Superheat (thermostat or metering device issue) or low mass flow (worn out compressor)

    I assumed we are talking AC compressors, as most hermetic piston compressor tops are suction gas cooled (refrigerators and freezers)
    Last edited: Apr 26, 2017
  6. Capt Ralph

    Capt Ralph Senior Member

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    Without a high side reading were still guessing. The low side is a bit high. I have witnessed a flooded (to much Freon) compressor that was cool.
  7. Knight

    Knight Member

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    Low refrigerant will over heat compressors. It's leading cause of compressor failures along clogged condensers which is not the case in boat with water cooled condensers. You could have a restricted cap tube or txv. Not knowing high side it's easy to over charge. Checking super heat will tell you a lot.
  8. CSkipR

    CSkipR Member

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    The high side was 185. The superheat numbers were both about the same number 42 (maybe 4 deg difference) which I'm thinking should be 10-12 if I remember correctly. Will check around the evaporator and vents for any kinks. It seems to be cooling okay but not great.
  9. Knight

    Knight Member

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    Is it water cooled or air. And what's ambient temperature. It could be an inefficient compressor but it wouldn't be cool to the touch. If its r22 I would think 240 to 275 on head. I'm not to familiar with marine applications but every time I've had a cool compressor it's overcharged, froze up or bad txv. Cap tubes just clog up.
  10. CSkipR

    CSkipR Member

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    Water cooled ambient temp 80.
  11. Knight

    Knight Member

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    By your ambient and pressures it seems low. But compressor is unusually cold for some reason. How long does it run before you check temp. Super heat should be high too. Bring your head up to 240.
  12. wdrzal

    wdrzal Senior Member

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    The high side is not as relevant as the low side pressure. you are correct, More than 50% of ac units are overcharged. I usually need to remove gas in a lot of cases for them to function correctly. Flooding is the reason why you need to understand what superheat is and consult a pressure/temperature chart to charge correctly. Thermodynamics is one subject wear common sense doesn't always apply.
    Last edited: Apr 26, 2017
  13. Knight

    Knight Member

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    185 high. 65lbs on suction is about 38 degree coil temp which is to low. 55 to 60 is about right
  14. CSkipR

    CSkipR Member

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    The compressor was running at least an hour when I checked it. So what is the recommendation to raise the compressor temperature? Remove some r22?
    My other ac unit cold suction line is 65 and runs well but the high side is definitely higher and the compressor top is over 100.
  15. Knight

    Knight Member

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    Are you sure there's no air restrictions, dirty filters.....
  16. wdrzal

    wdrzal Senior Member

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    The compressor with the lower temperature is the one with the problem........If you have a volt/amp meter measure the voltage of both compressors, They should be the same. Now measure the amps of both. multiply volts x amps = watts. multiply watts x 3.412 to get btu's. (1 watt =3.412 btu). All the electrical current is turned into work and given off as heat. This is part of the heat of compression. The rest of the heat is absorbed by the evaporator. You need specialized equipment to measure that. You already posted the suction pressure, measure the temperature of the suction line where it comes out of the evaporator so we can calculate the superheat. Superheat is often described as " hidden heat" since it can't be measured with a thermometer. You may want to google and print out a pressure/temperature chart for R22. This is required to calculate Superheat.


    I would bet the amps are lower on the cool compressor because its not doing as much work.

    If its overcharged the amps will be higher than the RLA (running load amps) or FLA ( full load amps).You need to find these numbers from the compressor data sheet. some compressor manufactures don't give both because they are very close together. There will always be a LRA (locked rotor amps) This is the maximum amperage the compressor can draw under any conditions.
    You really only need the high side pressure to calculate sub-cooling. You only need a few degrees to be sure the Freon coming out of the condenser is in liquid state until its gets to the metering device.
    Last edited: Apr 27, 2017
  17. Knight

    Knight Member

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    I disagree head pressure is just as important. Systems get overcharged by only reading low pressure while charging with clogged condensors, air flow issues or evaporators. Over charging, one or both of the pressures will be high depending any other issues. I own an hvac/refrigeration company. We only see less than 5 percent overchaged. One reason is there are more competent techs in my area or less jack legs. Without overcomplicating it pressures will get you through most any issues but always check coils, mechanical items like fans tstats compressors before hooking up. Most people hook up the guages for no reason.
  18. CSkipR

    CSkipR Member

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    No restrictions and all filters are clean. I have the r22 press/temp chart in my manual and that's what I've been using. I have the superheat at 4 degrees which I believe is low and should be around 10-12 although not sure if this is creating the cold compressor top.
  19. Knight

    Knight Member

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    Check your superheat and subcooling. Make sure your checking temps correctly at proper locations. If it's that low your flooding evap. But I would think your pressures would be higher if over charged. Both pressures are low in my opinion. Adjust charge see what you get
  20. wdrzal

    wdrzal Senior Member

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    Your correct about the superheat, it should be higher. High head pressure does matter, but a overcharged unit with high head pressure will show up on current draw which is easy to check without accessing the system .That's why I explained RLA & FLA

    I too think your under charged, unless you have Copland scroll compressors. 70% of them failed in under 5 years (low mass flow, in original units they used bushings instead of bearings. the bushings wore ,wearing out the edges of the scroll) They did give a ten year warranty and covered all them. Just need more info before a diagnoses can be made