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  1. #1
    Newbie
    Join Date
    Sep 2012
    Location
    Wilsonville, OR USA
    Posts
    3

    Default 1990 GMC Suburban heater stuck on

    I have a problem with the heat being stuck on all the time on my 1990 GMC Suburban. It doesn't matter where I set the temperature control or the mode selector. Several things seemed to fail all at once:

    Heat stuck full on
    A/C compressor will not come on
    HVAC controls don't seem to affect anything.

    I've replaced the mode switch and the vacuum switch, checked the vacuum lines and control cable, and replaced the vacuum source line up to the manifold. I've been seeing references to the Air Blend Door actuator in online searches, but my Chilton manual doesn't mention anything about it. I'd appreciate any direction folks could offer on this - it's too hot to have the heater on all the time!
    --
    Dennis Weatherly
    Wilsonville, OR USA
    1990 GMC V2500 Suburban SLE

  2. #2

    Default

    It sounds (to me) like the air blend door, but I'm afraid, I din't have any experience with the '90 fullsize.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  3. #3

    Default

    remove the glove box, you should see where the heater coil is (inside that big plastic box)
    On top, there is a rod to control the opening. Mind has a lose plastic so I use a new eye hook to fix the problem. hope that's your problem.
    AC compressor not turning on, I have no idea.
    does your fan speed work? Mind wasn't, only High so I replaced the resistor as well.

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