intermittent a/c automatic on issue

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Abel, Oct 28, 2012.

  1. Abel

    Abel New Member

    hey guys. ive got a 2000 silverado 1500 that ive had for almost a year now.
    i honestly only notice it in the winter-ish months because thats when you dont want a/c. and during the hotter months i just leave the a/c on. but sometimes when i start the truck it will automatically kick a/c on and you cannot turn it off by pressing the button. it lights up a/c and will blow cold air.. regadless of it being on full heat!
    the only way to get it to blow heat is to turn the truck off and restart it. then its fine. it usually only does this once per trip. it wont go back to a/c again automatically but you can turn it on/off manually as you should.
    just wondering if anyones had this same problem? thoughts? fixes?
    i work for a dealership and have access to other techs/info/etc. but just thought i'd run this through the silverado forums and see if its been a problem to anyone else.
    i havent looked into it yet but my initial guess is that it may just be a faulty HVAC control unit. so i might look into replacing the unit itself and see if it does it anymore.
  2. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    Sounds like a bad blend or mode door actuator. The next time it happens check to see if it is only one side (driver or passenger) blowing cold. If is specific to one side then it's the blend door for that side. I've got a write-up here on how to do the passenger side (which is the harder of the two), and you can find it easily enough with a quick search on GMTC. The driver's side is far easier and write-ups for it are easily found via Google.
  3. Abel

    Abel New Member

    thanks for your help! ill look further into it and see what i can figure out. i need to check for any kind of bulletins put up about this
  4. Abel

    Abel New Member

    hey guys been busy with work havent had time to work on my own stuff yet, found out that the cause of this happening is due to my truck having HID headlights.. and its something to do with my DRL/automatic lights.. since ive owned it, ive not been able to run just the parking lights unless its in DRL mode.. also its due to when i turn the truck on and switch it from high-beams to HID's is when it switches over to A/C
  5. j cat

    j cat Epic Member 5+ Years 1000 Posts

    I have the same vehicle . same yr. manual ac controls. sometimes in winter when it gets very cold the ac comes on by itself and its locked up in ac mode. only cold air.

    I disconnect the negative battery connection and turn key to on which drains the voltage. then reconnect. happens at least once every winter. been doing this for all its life.

    must be some kind of system logic failure. that needs to be reset.

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