88 firebird Air stuck on defrost. Where is the vacuum pump?

Asked by May 27, 2013 at 02:18 AM about the 1988 Pontiac Firebird STD

Question type: Maintenance & Repair

My son bought an 88 firebird. The air is stuck on defrost. It looks like it all runs off of vacuum lines but I can't find the pump or other solution.

2 Answers

65,975

You're correct. It is vacuum operated. There is a vacuum hose that connects to the intake manifold. Yours must be broken or disconnected. In the engine compartment look for a single vacuum hose coming out of the firewall. Usually near the center or perhaps closer to the drivers side. There is no vacuum pump for this. It hooks directly to the intake manifold. There should also be a small, usually white, check valve in line. Almost looks like a small round disk. This check valve is there to prevent mode shifts while accelerating and decelerating. HTH. -Jim

Best Answer
109,965

If vacuum line to intake is ok I would check behind your ac control unit under the dash. I believe you will fine what I call a five way vacuum deverter that controls your flaps in the duct work. Your main vacuum line feeds it. When they go bad you will only have defrost. With the age of your car I would suspect it needs to be replaced. Hope this helps

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