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Thread: Help with AC Compressor

  1. #1
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    Help with AC Compressor

    In need of some expert advice here. The compressor seams to be losing power and shutting down randomly. After disconnecting and reconnecting it begins to work again until the car is turned off and then wont reengage. Time for a new compressor or just a control unit thing? Any thoughts would be appreciated.

  2. #2
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    The first thing is to check the refrigerant charge. Your symptoms correspond to an overpressure safety shutdown usually caused by low refrigerant.

    Brett

  3. #3
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    Watch the auxiliary fan - if that is running so should the compressor - aux fan not running = compressor not running.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  4. #4
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    Quote Originally Posted by ltbrett View Post
    The first thing is to check the refrigerant charge. Your symptoms correspond to an overpressure safety shutdown usually caused by low refrigerant.

    Brett
    Thanks, refrigerant was fully charged during testing.

    Sent from my SM-G950U using Tapatalk

  5. #5
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    Quote Originally Posted by Timm View Post
    Watch the auxiliary fan - if that is running so should the compressor - aux fan not running = compressor not running.
    Aux fan working as it should. Going to check to make sure there is no belt slippage next but oddly, compressor works fine when cold but shuts down after it warms up...5-10 minutes after running.

    Sent from my SM-G950U using Tapatalk

  6. #6
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    What you are describing still sounds to me like a safety shutdown. You need to monitor both high and low side pressures from a cold start to shutdown to really see what is up.

    Brett

  7. #7
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    Quote Originally Posted by ltbrett View Post
    What you are describing still sounds to me like a safety shutdown. You need to monitor both high and low side pressures from a cold start to shutdown to really see what is up.

    Brett
    That's what I thought. Thanks!

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  8. #8
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    Quote Originally Posted by ltbrett View Post
    ...You need to monitor both high and low side pressures...
    I must inject a nuance which is that operations don't care what a technician gauge set says the pressure is, but rather what the controller box thinks it is.
    So for this troubleshoot the seasoned technician will be looking primarily at the output of the pressure switches with a 2nd opinion or reference measurement coming in from the gauge set.
    IOW's sensing could be funky.
    ****
    Probably not related to this BMW case, but some compressors, like on my MBZ, have a compressor speed sensor, to check for slip and overspeed.
    In such a case I would be checking for (electrical) noise or drop out.
    ****
    Also wondering if any of this sensing or faults would show up on scan codes.

  9. #9
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    Good stuff...makes total sense. Unfortunately nothing on the scan.
    Quote Originally Posted by Hyper View Post
    I must inject a nuance which is that operations don't care what a technician gauge set says the pressure is, but rather what the controller box thinks it is.
    So for this troubleshoot the seasoned technician will be looking primarily at the output of the pressure switches with a 2nd opinion or reference measurement coming in from the gauge set.
    IOW's sensing could be funky.
    ****
    Probably not related to this BMW case, but some compressors, like on my MBZ, have a compressor speed sensor, to check for slip and overspeed.
    In such a case I would be checking for (electrical) noise or drop out.
    ****
    Also wondering if any of this sensing or faults would show up on scan codes.
    Sent from my SM-G950U using Tapatalk

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