HVAC stuck in Defrost

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Thread: HVAC stuck in Defrost

  1. #1
    Walking
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    HVAC stuck in Defrost

    I have a 2003 Silveraldo 2500 HD. After a power loss to my AC controller (pulled it from the dash to work on the radio) air will only blow from the defrost. Controller shows correct settings. After starting the engine with the vent selected to front vents, air will blow out of the proper vent for about 10 seconds and then switch to the defrost vents and stay there.

    I pulled the HVAC/ECAS fuse for 10 seconds and restarted... The AC didn't correct itself...

    I have auto HVAC controls with dual climate zones.

    Any thoughts?

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  3. #2
    6.2 Liter LS3 V8 drew630's Avatar
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    Re: HVAC stuck in Defrost

    I can't for the life of me think of the name of the switch that controls this but this is a very very common problem in these trucks. That switch will have to be replaced.

    Edit:
    Here is the thread I started when mine was doing something very similar and its full of good information:
    HVAC control problem

    Mine ended up being replaced a couple months later when it went into constant defrost mode. The software update didn't work either (although it might on yours).
    Last edited by drew630; 11-27-2008 at 05:13 PM.
    2014 Silverado Z71

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    1.8 Liter ECOTEC Sandhopper's Avatar
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    Re: HVAC stuck in Defrost

    Drew630, what did that end up costing you... My dealer just quoted me $600 to replace the HVAC actuators on my 04 Silverado... Is this some thing that the average person can tackle? Thanks

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    6.2 Liter LS3 V8 drew630's Avatar
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    Re: HVAC stuck in Defrost

    Mine was goodwill'd so I don't know how much it would have cost. As for whether it is something an average person can do or not I have no idea either. Sorry.

    Try sending either GMCSonoma or shadams a pm and see if they can help with your questions (if they don't respond to this thread that is). Both of them are very knowledgeable of GM products and service.
    2014 Silverado Z71

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    Re: HVAC stuck in Defrost

    2000 Chevy C/K 3500 crew cab long bed dually with ALL computer wiring deleted and engine replaced with 700 hp NASCAR engine normally aspirated. Problem: HVAC controller works fine if "recirculation" and "a/c" buttons are in OFF position, i.e. fan speed knob works fine, temperature knob works fine, and air exit level to cab works fine, BUT if either the recirc. or a/c buttons are in the ON position, the first two knobs (fan speed and temp.) work fine but the output level reverts to either the defrost level or the floor level, i.e. none of the three intermediate levels will work. Questions:
    1. Does the HVAC controller work through the VCM (vehicle control module)?
    2. Is it likely that one of the HVAC actuators may be malfunctioning?

    ANY help will be most appreciated although we can circumvent the problem with a switch, we hate to do this on a truck in which we have invested some $75K more or less. Thanks very much, Charles 865-588-0372 H or 865-368-8254 C. If you feel fairly sure you know the answer to the problem, send me your first name and a phone number and I will call you so it will be at my expense. You can e-mail me at cmoss3@bellsouth.net Thanks for any help.
    Last edited by oldroder; 04-06-2009 at 04:40 PM. Reason: Add new last sentence.

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    2.4 Liter SIDI ECOTEC Regalguy96's Avatar
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    Re: HVAC stuck in Defrost

    Having this same problem with my Regal currently. I can get all heat settings when I press the button of course the light will light up, but when I switch to A/C on any setting it will blow for awhile out of the medium/max and other a/c settings then switch to floor all by itself. Went to the pick and pull last weekend and was lucky enough to find another unit (the only one in the yard with dual climate control) so I will try that first, if not no A/C this summer.
    Current Ride:~2002 Chrysler Sebring LX Convertible~

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    1.4 Liter Turbocharged ECOTEC ensign83's Avatar
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    Re: HVAC stuck in Defrost

    there is usually a fan control module in the firewall and inside the hvac duct that causes this in many GM cars. in my Olds, the fan went fullspeed thru the defrost, even with the key off!
    Mike, 1990 Olds Trofeo FE3, and 1998 Camaro 3800 5sp w/ Borla and Whisperlid

    Western Shore of the Chesapeake

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    Re: HVAC stuck in Defrost

    Hi,

    I also have the same Problem with my 03' Chevy silverado, but it is a 1500,
    i was wondering if you had ever fixed the problem and if so what did you do?

  10. #9
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    Re: HVAC stuck in Defrost

    I had a similar issue. Air would only blow out of defrost vents after I replaced my battery. But this worked for me:

    1) Unplug HVAC fuse for 10-30 seconds
    2) Start truck
    3) A/C comes out defrost - wait about 10 to 15 secs
    4) A/C then starts coming out the floor vents for about 5 seconds
    5) A/C then starts coming out the dash vents.
    6) While the A/C is coming out the dash vents, turn A/C OFF (otherwise it cycles back to defrost for good).
    7) Turn truck OFF
    8) Restart truck and it should work fine

    (Found solution on another forum from user "ccurran")

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    4.4 Liter Supercharged Northstar Tomko's Avatar
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    Re: HVAC stuck in Defrost

    Quote Originally Posted by farago2r View Post
    I had a similar issue. Air would only blow out of defrost vents after I replaced my battery. But this worked for me:

    1) Unplug HVAC fuse for 10-30 seconds
    2) Start truck
    3) A/C comes out defrost - wait about 10 to 15 secs
    4) A/C then starts coming out the floor vents for about 5 seconds
    5) A/C then starts coming out the dash vents.
    6) While the A/C is coming out the dash vents, turn A/C OFF (otherwise it cycles back to defrost for good).
    7) Turn truck OFF
    8) Restart truck and it should work fine

    (Found solution on another forum from user "ccurran")
    Welcome aboard farago2r and thank you for this contribution to our GMi community.
    Tomko

    Current Fleet:
    2014 Cruze Diesel (daily grinder)
    2008 DTS Lux III (pleasure craft)
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    Retired Fleet:
    1999 Tahoe PPV (14.5 years / 135,879 miles)
    1988 Caprice 9C1 (first new car)
    1984 6000 STE (first car)

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