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1999 Grand am, directional vent door not working

ehenry1969ehenry1969 Posts: 3
edited December 2016 in Pontiac
The 5 fan speeds, and the temp control work fine, but control for the vent, defrost does not change. The air blows out of the the front defrost and the vent at the same time. ???


  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    You can actually scan the HVAC for possible trouble codes on this problem. Sounds like you might have a bad actuator, which you can sometimes find by locating the blower motor under the dash and then following the wires back to the actuator.
  • Thank you much , I'll look into that
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 24,030
    edited December 2016
    It may be a bad actuator (vacuum motor). They have a rubber diaphragm that pulls a rod to move a vane (door) inside the heater box when vacuum is applied to that line. You'll have to spend some time lying on the floor and looking up under the dash and seeing if you can move each actuator and try to figure out what each one does.

    But first, you didn't mention it as part of your problem, are you able to direct the air to the floor? Although the physical design of the heater box I looked up for a 1999 Grand AM is different, the vacuum unit will operate much as my leSabres did. When there's no vacuum, the unit goes into defrost so that the air can always go to the windshield to clear it for safety. It takes vacuum to move each of the other vacuum diaphragms to a different setting from that default.

    Check to see if you are getting vacuum into the HVAC in the car. Look under the hood for small, 1/4 inch, vacuum lines that go into the intake manifold. If any work was done under the hood recently, that line may have been pulled off. Sometimes they are rubber and deteriorate due to the heat where they are really close to the motor.

    Also, the vacuum from the intake manifold goes to a storage bottle or tank so the HVAC operates on that vacuum when the engine is accelerating and intake vacuum drops. That tank may have cracked so that it leaks the air in losing the vacuum. Or the line onto the tank may be damaged or not snapped on.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

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