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  1. #1

    Default heater and a/c problem

    Hello all,
    I just inherited a 1996 Suburban with 200,000 miles from my parents.
    It is wonderful but I am having a strange problem.
    The car only blows very hot air through the vents regardless of the position of the dials.
    That's not the strange part. But this is: I just realized that the heater/ac works perfectly when the headlamps are not on. As soon as the light switch is turned on, the a/c and or recirc. button go off and it's back to just hot, hot hot.
    What's going on?
    I should mention that the daytime running lights have not worked for some time.

    Thanks in advance

  2. #2
    Jr. Engineer Gmcsuvguy's Avatar
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    Dec 2007
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    279

    Default

    That sounds like a fun one...Not having a schematic of your truck it is hard to diagnose. You would have to find out what those two have in common. Maybe there are some melted wires in a harness somewhere that are backfeeding when the lights are on...Goodluck!
    Ken Beida
    2010 GMC Sierra Crew Cab 4X4, 5.3L
    2009 GMC Sierra Denali, 6.2L = 403hp, AWD, Full load

  3. #3

    Default

    If it changes from hot to cold normally...Whenever....The mode control motor is fine.
    The circuts are fairly simple on a 96
    More than likely it sounds like youve got a control head problem.
    Check the plugs, to the control for any dammage...loose connections ect.
    If ya know how to use a test light, I would identify the IP backlighting voltage signal to the control head (usually grey in color) Lights the testlight whenever you turn on the headlamps.
    come off the connector a couple of inches and cut it...Retest your problem...If that fixes your problem...Put the wires back together and buy a new control head. Good luck

  4. #4

    Default

    O yea.......Im dont remember 96s havin DRLs
    I am allittle burnt

  5. #5

    Default

    my 98 did! Theres a DRL fuse in the fuse box left of the IP I pulled mine.
    If ya got a green lamp indicator on your dash and it goes out when you turn your headlamps on.You got-em
    If the fuse is good.....You need a DRL control mod. Under left center of your dash...Its black metel with heat sink fins....It blows to change as designed.......If ya REALLY want-em to work, Ill pass on a trick to changin it

  6. #6

    Default

    Quote Originally Posted by 30 Yr GM Tech Burn-out View Post
    my 98 did! Theres a DRL fuse in the fuse box left of the IP I pulled mine.
    If ya got a green lamp indicator on your dash and it goes out when you turn your headlamps on.You got-em
    If the fuse is good.....You need a DRL control mod. Under left center of your dash...Its black metel with heat sink fins....It blows to change as designed.......If ya REALLY want-em to work, Ill pass on a trick to changin it
    Thanks for the suggestion. I don't care about having DRLs. But I mentioned it because I thought maybe the problems were related. You made reference to the "IP" can you tell me what that is?

    Thanks again

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