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**Help with a GM defrost problem**

Discussion in 'Off Topic Threads' started by Bvr Tail, Sep 30, 2011.

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  1. Bvr Tail

    Bvr Tail Well-Known Member

    Joined:
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    Messages:
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    I need input on a problem with the defrost cycle of a 1999 Buick Century.

    The inside air blows out the vents no matter where you put the control.

    I recently switched over to defrost, but all air still came from vents.

    All locations of heater control have same result.

    Just as background, this car has set for a while, and I bought it from an estate. No mouse/rat damage, and everything is clean as a pin.

    It has 23,000 miles on it and is in excellent shape.

    It was set on A/C when I bought it, and I had no reason to change it until now for colder weather.

    I was told this model uses vacuum to switch this defrost door, and electric motors for other doors?

    Also was told to check by the battery for a pinched/corroded vac line.........no problem there.

    I figure the defrost door is stuck, but as I am a large guy, I find it hard to get in position to inspect it, but if I had some clues, I can get it fixed..

    Any help?
     
  2. Bvr Tail

    Bvr Tail Well-Known Member

    Joined:
    Jan 29, 1998
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    Please give advice if you can really help with a heater/defrost problem with a 1999 Buick Century

    The air all blows out the vent and nowhere else, no matter where the selector is.

    I can hear air changing a bit when I switch to max air, but ho heater or defrost mode.

    I was told to check the small vacuum line by the battery for pinched/corroded areas. Checks OK

    This car has 23,000 miles and has set for a while with the controls in A/C mode.

    No mice/rats/ground squirrels as it was in a secure garage.

    Any help?

    Thanks

    Danny
     
  3. Shooting Coach

    Shooting Coach Well-Known Member

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    Describing the problem might help.
     
  4. Remstar311

    Remstar311 Member

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    There are a bunch of professional and back yard mechanics on here that will help but are not likely to email you.
     
  5. Bvr Tail

    Bvr Tail Well-Known Member

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    Original request updated!

    Thanks in advance

    Danny
     
  6. Catpower

    Catpower Molon Labe TS Supporters

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    Not going to be much help, but you have either a stuck damper (probably) or a vacuum leak, not allowing enough vacuum to get to the actuator to move the damper.

    Now you just need to find the stuck damper, or vacuum leak
     
  7. Conn. Man

    Conn. Man Member

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    Brv Tail,You have a personal message .

    Sandy Holehouse .
     
  8. AveragEd

    AveragEd Well-Known Member

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    You don't have a vacuum leak - for safety reasons, all GM HVAC systems are designed to default to the "defrost" duct door setting under conditions of no vacuum.

    Ed
     
  9. Shooting Coach

    Shooting Coach Well-Known Member

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    What Ed said.

    Look for something jamming door, or bad vacuum switch at controller.
     
  10. Bvr Tail

    Bvr Tail Well-Known Member

    Joined:
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    Found it!

    I noticed once that when I moved the A/C-Heater control, it was rather stiff, but loosened up after turning a few times

    As I said, this has set for some time, and after checking all vacuum sources, and connections inside and out, I removed the control.

    I'm rather inquisitive, and so I took it apart. I found the rubber seal that separates the chambers at the ports had came loose, and moved, thus not letting the vacuum to the right ports at the right time.

    Re-installed seal, a dab of light lube on surfaces, installed back into dash and back in business.

    Thanks

    Danny
     
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