Wierd AC

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  #1  
Old 08-17-09, 12:27 PM
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Wierd AC

1994 Buick PAU, FWD, Auto

My ac randomly decides to blow out of the defrost vents rather than the passenger ones. I cannot determine any sort of trigger for this. It blows fine, then switches, and if I'm lucky it switches back. So far, I haven't had the car turn on and blow through the wrong vents, it always seems to start properly.

Length of drive doesn't seem to be a factor.

All my belts appear to be tight and in good shape. Spotted one with wear a month ago and had it replaced, but this has only been occuring for about a week.

Anyone that could point me in the right direction would be greatly appreciated.
 
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Old 08-17-09, 02:26 PM
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I believe there's a one-way vacuum valve that can go bad and do what you're experiencing. I'll bet it does it when you stomp on the gas.

Any fault in the climate control vacuum and the system defaults to defrost. It's a safety feature.
 
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Old 08-17-09, 05:04 PM
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Yup, like Kestas said, sounds like a vacuum problem. If the mode door actuator is not getting vacuum, it will default to the defrost position.
 
  #4  
Old 08-17-09, 05:51 PM
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some of these cars are equipped with a programmer module that controls the the routing of the vacuum (is located under the passenger side dash) First check the vacuum source to the unit most of the time a purple hose, then turn the control unit to dash/ vent and check vacuum on the blue hose, this hose goes to the valve that controls the air delivery, if the programer has vacuum, but not routing vacuum to the level valve when switched to vents then you might have a bad programer.
 
  #5  
Old 08-23-09, 08:20 PM
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Thanks all... had to repair a small hole, cured it right up!
 
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Old 08-23-09, 10:43 PM
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Originally Posted by Kestas View Post
I believe there's a one-way vacuum valve that can go bad and do what you're experiencing. I'll bet it does it when you stomp on the gas.

Any fault in the climate control vacuum and the system defaults to defrost. It's a safety feature.
yes this is correct. verified!
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