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Intermittent AC failure

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  • Intermittent AC failure

    So in the last couple months I've had this happen 3 separate times. I'm using the AC, and all of a sudden the idle climbs because the compressor clutch disengages.

    The first time I was sitting in a parking lot idling while on lunch. AC was on, at normal high idle, then the clutch disengaged and the idle climbed to 1500+ RPM. Turning off the AC brought the idle back down, and turning it back on did not restart the compressor. I turned it off and went inside.

    The second time I was driving, and noticed the air getting warm. I turned the AC off and then back on a few minutes later, and it worked fine the rest of the day.

    Then today, I was sitting at a light, turned left, and then stopped to prepare for another turn and noticed the idle didn't come back down, and sure enough, warm air from the vents. Cycling the button turned it back on for a few seconds, and then it did it again.

    The majority of the time it works pretty well.

    It seems to me that the compressor clutch is disengaging but the ECU still thinks it's on, so it maintains high idle but without the compressor load it idles way high. I'm thinking it may be a failing relay, or maybe the compressor is overheating and turning off? Do our compressors have thermo switches? And would it just disengage the clutch, or would it tell the ECU to turn off the AC?

    The car is an '01 LS. If you have any other questions ask away.

    Thanks in advance!
    Chandler Bishop

    Sunlight Silver/Tan '01 LS

  • #2
    Thermoswitch on the evap core (under the dash) to prevent icing up, low pressure switch on the low pressure line, high pressure switch on the compressor.

    On the NA (but I doubt the NB is more complex), the a/c switch on the hvac panel goes to the ECU (to enable idle up), ecu enables the compressor relay - and all the above mentioned switches are along the way from the ECU to the relay, so if any one of them opens the relay disengages. Dead simple.

    So, annoyingly - you'll probably need some a/c gauges to figure this one out. But of course, the most likely answer is you need a (small) recharge.
    Last edited by iscariot; 08-19-2017, 01:30 AM.


    • #3
      Here's some back story. After I bought it, as the summer came and the temps rised it started to quick cycle. I had it looked at and it was slightly over charged so evacuated and recharged it to the proper level. When it was quick cycling, the ECU was cycling the high idle along with the compressor. This is why I was leaning away from a pressure issue since the ECU seamed to know when the pressure was wrong and shut everything down, not just the compressor. I'll have it checked out for sure!
      Chandler Bishop

      Sunlight Silver/Tan '01 LS


      • #4
        I had an issue with my A/C where it would cut out intermittently. I had my clutch replaced at R-Speed and they noticed while I was there that the connector to the fan on my driver's side was burned out. They replaced the fan with a used one with a good connector and the A/C has been fine ever since... This may be completely unrelated to your problem, but it solved my A/C problem, so maybe worth looking into? I'm not too familiar with the whole system, but does it sound right to anyone that the fan cutting off would also cut off the A/C?
        Blue '99 with '01 header swap, Tein Street Advance, FM Exhaust, RPF1s