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  1. #1

    Default Why does my A/C compressor only engage on defrost - 99 Suburban

    Started today. The only way the compressor kicks in is in defrost mode. Do the controls need to be replaced?
    Danny
    Saint Petersburg FL
    1999 SUBURBAN LT C1500
    1985 MAZDA RX-7 BLOWTHROUGH TURBO
    1987 BMW 325IS
    1994 Infinti Q45
    1997 Nissan Maxima GLE


  2. #2

    Default

    If the AC works and pumps cold air out the defroster vent with the temp set to cold you probably have a bad switch. The easiest way to check the switch is to put a scanner on it. The scan tool data stream will show the state of the switch.
    Jim

    2004 SILVERADO 2500HD LS
    Pro Comp Leveling Kit
    285-75-16 Cooper ST All Terrains
    Pro Comp Programmer
    Bilstein Shocks
    Linux Bed Liner
    Tinted Windows



    Other rides:

    1967 Landcruiser <350 Chevy>
    1970 Camaro
    1990 Geo Metro Convertible
    2007 FJ Cruiser

  3. #3

    Default

    What kind of A/C system do you have?

    Auto?
    Manual?
    Front and rear? Rear working?

    What are your button settings when this is happening?
    92 GMC Sierra 2500

  4. #4

    Default

    Auto, front and rear work and the a/c button is pushed in. The a/c button only illuminates and the compressor kicks on only when the direction knob is set to defrost as soon as i turn the direction knob from defrost the a/c light on the a/c button turns off even though it is pressed in.

  5. #5

    Default

    Test the electrical connections on the A/C on switch. The contacts on this switch may be dirty and not making good contact.

    I don't know if this switch would be easy to get to or not?

  6. #6

    Default

    Jimmie, can autozone do that scan or is this a different scanner that can tell the state of the switches?

  7. #7

    Default

    Their scanner won't give that data. You need a GM scanner or a Snap ON style scanner that reads manufacturer data. Autozone just uses a code reader that gives generic OBDII data only. Most repair shops use the type of scanner that will read manufacturer specific data.

  8. #8

    Default

    a little off point but be glad your not in California. They had made it illegal for autozone to check your codes, so they switched to having the scanner part of their loaner tools. Well at the end of last year the a-holes in Sacramento made it illegal for them to even do that, so that you have to go have a mechanic check the code. It made me finally break down and buy my own. Ok rant done (sorry not much help for your actual question).
    David
    2004 Silverado 2500 Crew Cab 4x4, AMSOIL EA air filter, Granatelli MAF sensor, Throttle body spacer, Magnaflow exhaust (true dual to 2 in 1 out muffler), 6" ProComp lift (add a leaf and 5" superlift rear block), Bilstein shocks, 35's (Cooper Disoverer ST) and 4.10 gears, Rhino Liner, EGRUSA fender Flares and widow visors, extended stainless steel brake lines, firestone airbags w/onboard air compressor, Pioneer Avic X940BT navigation, Accel backup camera.
    http://www.gmtruckclub.com/forum/sho...Silverado-2500
    1960 Land Rover Series II 88
    2001 Pontiac Sunfire
    2013 Toyota Avalon Limited (Wife's Car)
    NRA Life Member

  9. #9

    Default

    Does the scanner loaner tool track the switch status or is that the simple obd ii tool?

  10. #10

    Default

    Scanners you buy at auto parts stores usually only scan the engine computer. Some newer models also scan the ABS and air bag computers. Some may scan additional things on the vehicle.

    Newer vehicles can have 25 different computers and 2 or 3 computer local area networks. Upscale vehicles can have near 80 different computers.

    A Tech II scanner with the right adapter (for GMLAN) can scan all of these. These cost $3000.

    For your A/C problem, this is just a simple switch which is wired in parallel with the defrost switch which also turns on the A/C.

    Try pressing firmly on the A/C switch and turn it on/off several times and you might get it to work.

    If you are going to invest in any tools, I would suggest buying a GM factory Service Manual set for your year/model vehicle, then you could look at the wiring diagrams yourself. Also get a multimeter.

    As to fixing this problem, perhaps you could go to a wrecking yard, find a vehicle with the same A/C control panel, take it apart and see how it works inside. See if there is a way to clean the A/C switch contacts.

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