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Cold AC compressor means what

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

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  1. wdrzal

    wdrzal Senior Member

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    But if the charge is low ,there's a leak....unless freon was lost from putting gauges on and off.......Knight you said in post 7 that a low charge will burn up compressors. When a compressor over heats the thermal cutoff shuts them down.

    Also CSkipR already said coils are clean and no restrictions a few times.
    Last edited: Apr 28, 2017
  2. 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

    Your low side pressure should be around 75 to 85 psi
    Last edited: Apr 28, 2017
  3. Knight

    Knight Member

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    It's not just the over heating, it's the lack of lubrication without the refrigerant flow. Also compressors can run to hot for long periods that causes failure. I've seen many hot compressors, enough to burn you that will run all day. Low and high pressure controls Will save a compressor time and time again. I've been doing this for 20 years and I've seen it all but I learn something new more that I could have known this late in game.
  4. CSkipR

    CSkipR Member

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    Outside air temp 80. On this compressor their are two evaporators. One for the front v berth and one for the master suite. I measured return air temps and vent temps and here is what difference I got. The master seems to be marginal but the front v berth is way off. Thoughts again.
    Front v berth - Return air 68 deg Vent 57
    Master suite - Return air 77 deg Vent 6
  5. wdrzal

    wdrzal Senior Member

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    There should be ~ 20 F degrees temp drop across the evaporator. The master is way off, at 6 degrees the evaporator coil will freeze solid. If a room is 80 you should get approx. 60 out a vent. As the room cools to 70 you should get approx. 50 degrees at the vent.
  6. CSkipR

    CSkipR Member

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    I on the SA$A ZBC v berth ac control the bottom knob turns the fan up/down. I'm not able to tell a difference in the fan speed so not sure whether its on slow or fast. Is there a way to bypass or check the 230v rheostat? Can I wire it so that its running on full speed by bypassing the knob? With an ohm meter should I notice a resistance difference as I turn the knob.
  7. wdrzal

    wdrzal Senior Member

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    You need ~ 400 cfm per ton.(12,000 btu). Too much airflow and you lose dehumidification. To low and the coil freezes solid.
  8. wdrzal

    wdrzal Senior Member

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    CSkipR did you use a infrared thermometer for the temps you posted ?
  9. CSkipR

    CSkipR Member

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    No I used a regular ac temperature thermometer.
  10. wdrzal

    wdrzal Senior Member

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    You can't use a rheostat to slow a AC motor. That will lower the voltage and burn it up. Many motors have 3 or 4 speeds using multi wire taps. A Triac "Modern dimmer" can slow a AC motor down. It doesn't lower the voltage , it changes the ratio of time on to time off to change speed. Think of turning a light switch on & off 100 times a second and the motor is at 100% speed. Now turn the switch on & off 80 times a second , the motor will be at 80% speed . Still getting full voltage. You can google Triac for more details on the circuitry.
  11. CSkipR

    CSkipR Member

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    Maybe rheostat is the wrong terminology but it came with the cruiseair system. I'll post a picture.

    Attached Files:

  12. wdrzal

    wdrzal Senior Member

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    One thing most people don't realize is if the evaporator temperature is low (say 6 f. or 30 f.), the unit will remove much much less heat (Btu's).than if the evaporator was 45F.

    I would need to see complete details containing all the Data of the compressor, condenser ,evaporator and piping diagram. Not sure yet if these units are also heat pumps. Plus a complete wiring diagram.Right now I don't even know if the metering device is a thermal expansion valve,pressure expansion valve or cap tubes. I would need very accurate high and low pressure readings and exact temperatures from 5 to 12 exact points, Just to get a basic picture of what's going on. We are not even sure if the problem is mechanical or electrical.