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AC compressor runs constantly

Discussion in 'General Chevy & GM Tech Questions' started by markf1971, Aug 21, 2014.

  1. markf1971

    markf1971 New Member

    I have a 99 Burb that I bought 6 months ago. I just got around to checking out why the AC didn't work. It had an obvious leak where the hose connects to the compressor. I cleaned up the outside, replaced the seals (washer w/rubber), pulled a vacuum on the system and it held (YESSS!). I charged up the system and it cools pretty good in all the front vents. However, the rear vents feel like ambient air temperature. My first guess was that perhaps the expansion valve for the rear evaporator core was stuck and won't open. Does anybody have any experience with this happening?

    Also, the AC compressor never cuts off. I have been cycling it off every few minutes via the "AC" button on the dash to keep things from freezing up. Any ideas on that?

    Thanks!
     
  2. jmcover

    jmcover Rockstar

    Before re-evacuating the system to swap out the rear expansion valve-

    -Double check the refridgerent charge.
    -Up Front: (with rear off) What's the outlet air temperature? Is it cold enough to suspect the thermocouple loop? Does the compressor cycle off when you turn up the (heat) temperature?
    -Out Back (with the front heat on) Rear Air temp? Does the compressor cycle?
     
    ChevyFan likes this.
  3. Chris Miller

    Chris Miller Rockstar 100 Posts

    The exact same thing happened on my '94 Suburban with the rear air. It's almost certainly the expansion valve. It's also a good idea to flush the heck out of the rear lines and blow the evaporator out with an air compressor. As for the compressor never shutting off, it could be either the clutch cycling switch or the cutout switch on the condenser.
     

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