Front defroster does not work

Discussion in 'General Chevy & GM Tech Questions' started by crashone, Feb 11, 2011.

  1. crashone

    crashone New Member

    Good Afternoon,
    I have a 1989 Z-71 whose defroster does not work. I get plenty of heat and full force fan from the center vents but not the top defroster vents. I changed the switch on the front of the "box" that controls an internal flap. I have the dash semi dismantaled but I do not see any other switches that may be the culprit. Can someone offer what else to check or what the real culprit may be?
    Thank you for the help.
  2. stephan

    stephan Rockstar 4 Years 5000 Posts

    Hey Crashone, welcome to the GM Truck club. I don't know if I can give you a solid answer on this, but is the switch actually moving the flap now? If the switch is working & you can see that it is moving the lever, maybe the lever is not connected firmly to the flap. Can you look in there with a mirror & a flashlight & see why the flap is not moving?
  3. crashone

    crashone New Member

    Thanks for the reply. I can move the flap by hand but can't tell if the switch is moving it or not. I found a site with an exploded view of the system and it shows 2 switches (actuators) for the different flaps. I'll have to check later and see if I can see another one.
  4. stephan

    stephan Rockstar 4 Years 5000 Posts

    When you move that flap by hand, does the air change to the defroster vents? If so then you know that is the correct flap & not the other one. If it is the correct flap then the switch is not connected to the lever for some reason, or the lever may have broken off the flap.
  5. inspectormatt

    inspectormatt Member

    Could be a problem with the control head itself. The motor down by the gas pedel is the one that controls where the air flows (panel vent, defrost vent, heat vent), you can remove the motor and move the linkage by hand to see if the flap inside is or is not working. By moving the linkage by hand it should change the flow of air from defrostor to heat to panel vents. If replacing that motor does not correct the problem then it may be the control head itself.

    COLIN DE Former Member

    Some makes and models do have heated windshields, not many, but some do. They do not have the wires like the rear window, and if they are cracked or broken they cost alot to replace, the technology is just not there yet to make it cost effectiv.
    Canopies | Portable Shelters | Pop Up Canopies
  7. mac0611

    mac0611 New Member

    go under the hood and check the vacuum lines at the cowl that come out of the vacuum amplifier. They rot and break common problem
  8. kennyb79

    kennyb79 Rockstar 100 Posts

    check and see if you can hear the flap closing when you switch it.

    I had the same problem with my my 89 a couple years ago,because it had sat for a while before I had bought it. It wouldn't switch to heater, just defrost...I finally ended beating the "box" with my hand while I operated the switch...whatever had caused it to stick freed it up and I haven't had an issue again....
  9. eaglescout89

    eaglescout89 New Member

    Does it actually heat up? Or is it luke warm. My vents stick from time to time, but it does switch.

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