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  1. #1

    Default Ac starts blowing out defrost on its own

    2007 NBS Sierra. Has the auto climate control. I'll be driving down the road and it switches from vent to defrost and I can't get it to switch back unless I stop and turn truck off. I guess it resets itself and then works fine. But it'll do it again in a day or two. I'm guessing the actuator is going bad. Anyone have an idea which actuator it is? I can see the one for recirculate and fresh air, I see the heat AC door actuator. There is one on very bottom of unit right above transmission hump in floor. I know the dash will most likely have to come out to fix it. Just need to know which actuator it is so I change the right one.

    ---------- Post added at 07:19 PM ---------- Previous post was at 05:22 PM ----------

    I think I found it. I believe it's number 20 right?

  2. #2


    Mode actuator is answer. Default mode is defrost so you can drive it in winter if it fails.

  3. #3
    Sr. Engineer
    Join Date
    Dec 2011
    11-22-boogie woogie avenue


    Try this first . Under the hood pull hvac/erac fuse. Wait 30 seconds put back.
    Start truck ..but do touch any ac or heat controls for 1 minute if this is the problem should set it back to factory default.
    Be good to go. If not will be the actuator at hump under dash.

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