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  1. #1
    Sr. Apprentice
    Join Date
    Aug 2010
    Location
    Whitehall, MI
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    31

    Default No heat - 1999 GMC Sierra

    Alright, I have a 1999 GMC Sierra 1/2 ton extended cab. When I have the HVAC controls on defrost, it works great. When I switch to vent, it cools off. When I switch to floor, it blows cold. Now, if I have the setting for defrost/floor the blows nice hot air at the windshield, and cold air out to the floor.

    I don't really know where to begin to look, but If I had to guess there is a servo or something that is failing. Any help would be appreciated.
    Thanks.

  2. #2
    Legend
    stephan's Avatar
    Join Date
    Sep 2010
    Location
    Far West, Oregon USA,
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    8,610
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    Default

    I'm no expert on these but I think it is the servo for the blend door.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  3. #3
    Sr. Apprentice
    Join Date
    Aug 2010
    Location
    Whitehall, MI
    Posts
    31

    Default

    I figured as much. It seems like that would be about right.. Any idea where it is?

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