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No air from vents...

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#1 Leylah


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Posted 15 July 2010 - 09:25 AM

I'm assuming this is a vacuum line issue? But what ones to check? The manual I have only has wiring diagrams... The defrost works & floor vents but not dash...any ideas?

#2 FBN Firebird Nation

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Posted 15 July 2010 - 10:18 AM

I know the tech article index has the vacuum diagrams for the HVAC system. Do you hear the air blowing? Which vents are the blowing from? What happens when you turn the selector knob for the vents?

#3 Ivan


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Posted 15 July 2010 - 12:12 PM

There is a motor that moves the air deflectors to change the airflow for defrost, floor or front vents, that mechanism is stuck or broken. It happened to my in a nissan and its a common AC problem. How to solve? I prefered to take to a shop.

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#4 1993TransAm



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Posted 15 July 2010 - 02:46 PM

I don't think the deflector is motorized in the 4th gens - I believe the climate control selector is vacuum operated. I can turn the selector knob when my car is off and still hear the hiss of the vacuum lines working. I believe you have a vacuum line problem. If you remove your radio trim piece, you can see the vacuum lines and the connector that plug into the back of your climate control. The lines are color coded flexible plastic tubes. I'd check to make sure your vacuum connector is snug in the back of your climate control. If that climate control face has been removed for any reason, that vacuum line connector has to come off. It's possible a previous owner may have disturbed the connection. I'd treat the vacuum issue just like an electrical issue...always start with the simple stuff first.

There are two 7mm bolts that hold the climate control in place behind the radio trim piece, one on each side. If you remove those and gently pull the climate control out a little bit, you should be able to make sure that vacuum connection is sealed properly. Just keep in mind that there are other connections behind that module, so I stress the word "gentle."

If you don't own a 7mm socket, I strongly recommend you purchase one. They fasten numerous interior trim panels in that vehicle and countless other GM vehicles from that era.
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#5 Injuneer


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Posted 15 July 2010 - 08:14 PM

The most frequent problem is a broken vacuum check valve (#38 in diagram).

4th Gen vacuum diagram, courtesy of Shoebox:

Posted Image

Other helpful info:


The HVAC control vacuum port is the one to the far right, above the vacuum connection for the fuel pressure regulator compensation line (nothing connected to it in photo):




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