A/C irratic function

Discussion in 'General Chevy & GM Tech Questions' started by RATRODKING, Oct 14, 2012.

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  1. RATRODKING

    RATRODKING New Member 100 Posts

    guys
    i have a 1990 k1500 4x4 with 5.7 engine.
    sometimes, in the past, with the a/c on, it would blow about 50% out of the vents, and the other 50% either out of the dash or down by the trans tunnel. i would hit on the lower unit, and the (flap) would close and it would them blow 100% out of the vents.
    but now its doing something different. its blowing about 25% out of the vents, and i can hear the blower blowing, like deep inside somewhere, but nothing is coming out from the trans tunnel vent or the defrost..
    what is going on here ? anyone have this happen to them before ? cant figure this new problem out.
    thanks guys
  2. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    The air is diverted using doors (mode doors), you may have one sticking.

    The newer trucks use electric motors, before that, the motors were operated by vacuum, I don't know when they changed over

    Try searching the site for mode doors
  3. RATRODKING

    RATRODKING New Member 100 Posts

    thanks much.. i will search for "mode doors", when i get home from work..
  4. SurrealOne

    SurrealOne Former Member 1000 Posts 100 Posts

    I've done both the passenger and driver's side actuator replacements on my 2004. Sadly I have no clue if that knowledge translates/transfers to a 1990 K1500. :(
  5. RATRODKING

    RATRODKING New Member 100 Posts

    OK guys,
    after searching on here and the internet, yes, it seems as if the mode door actuator is my problem.... it really only pops up every few months or so, but i think i will replace it anyways, since it is so easy to access....
    thanks guys
  6. RATRODKING

    RATRODKING New Member 100 Posts


    ok guys, it was good all week, and acted up today again.
    earlier in the week, i marked the actuator thats over the trans tunnel, on the left side of the box. i marked it when it was all working fine, blowing 100% out of only the vents.
    today when it was acting up, blowing less than 50% out of the vents, but nothing out of the defrost or lower trans tunnel opening, for the heat, i looked at my marks and that actuator is opening in the same position as when it was working fine, so it cant be that actuator.
    i found a drawing and see there is a "temperature actuator" thats located in the middle of the unit. could that be my problem ?
    on that drawing it does not show a right side actuator, mounted right next the the blower motor, on the passengers side...
    what does that actuator do ? again, my drawing i found online doesnt show that actuator.
    the cooling system is working fine, dripping a lot of condensed water through the drain tube and onto the ground.
    its driving me crazy....... please help.
    thanks guys
  7. SurrealOne

    SurrealOne Former Member 1000 Posts 100 Posts

    I wish I knew how to help you, but my knowledge is limited to the 99-06 (and 07 classic) years, as that's what I own and have worked on. :(
  8. RATRODKING

    RATRODKING New Member 100 Posts

  9. RATRODKING

    RATRODKING New Member 100 Posts

    ok guys,
    i laid up under the passengers side dash today and that actuator really looks like a pain to change out. no room to get at the screws. i have marked the position its at when its working correctly, so next time it acts up, i will see where the shaft is in relation to my mark.
    also i figured out that the next time it does act up, i will try cycling it through the three positions of defrost, vents, and lower trans tunnel vent, to see it i can "un-stick" it and get it blowing through only the vents.
    just dont want to change it out, since its so hard to get to.
    thanks
    [​IMG]
  10. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    Recirc is the function that switches between inside air and outside air. When recirc is on, the inside air is recirculated through the heater/ac vents. when recirc is off, outside air is drawn into the vehicle.

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