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Thread: AC Problem after LS Swap

  1. #1
    Join Date
    Feb 2018
    Massillon, OH

    AC Problem after LS Swap

    1989 C1500 with an 05 5.3, drive by wire throttle, R4 AC Compressor.

    I didnít have any AC issues before the Swap, I left the Compressor hooked up with the system charged and I mounted the R4 compressor with a Dirty Dingo bracket. I used all the stock wiring, but I donít remember if or how I tied into the engine harness. Iíll have to go back and look at the pin diagrams to refresh my memory.

    When I turn on the AC, the engine seems to stumble and the tensioner starts to bounce rapidly. I talked to a few people, I had the system evacuated, swapped the compressor, had the system recharged and still having the same issue. Iím on the verge of trying to track down a restriction in the AC system, dryer/oriface tube/blocked condenser etc.

    Is there any chance this is a PCM issue and not an AC system issue? I donít have a problem with replacing the dryer and oriface tube to check for a blockage, but I want to make sure I rule out a PCM issue before I start spending a bunch of $$$$.

  2. #2
    Join Date
    Oct 2019
    Is the R4 being turned the same direction as it was originally (not sure if the R4 has to turn only counterclockwise)? Also the idle airflow is increased in response to increased loads placed on the engine, so things like charging system loads, power steering load, AC compressor load, all cause the PCM to change idle strategy...so yes the new PCM may be the cause.

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