Need Help w/ Vacuum or AC Duct Problem

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Jul 24, 2011 | 09:46 AM

tperk100

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Junior User

Joined: Nov 2006

Posts: 92

Likes: 1

From: Virginia Beach, VA

Need Help w/ Vacuum or AC Duct Problem

MAX AC is on. After shutting down my truck for a few minutes, and then re-starting it, the MAX AC air is exhausted through the DEFROST duct. After about 5 minutes of driving I can hear the ductwork damper(?) straining but moving into what is probably the correct position. The AC seems to be working correctly as it blows all air out of the AC registers at this point.

What is perplexing me is that the thing starts to work correctly after a few minutes. If the vacuum or the damper were defective, you would think it would be that way full time.

I suppose I could start by asking how the AC duct system USED to maintain the damper position when things were working right. Is there some sort of vacuum reservoir that should maintain vacuum with vehicle shut down....therby keeping damper in correct position?

Any other thoughts / suggestions?

Thanks

Jul 24, 2011 | 09:52 AM

dchamberlain

Lead Driver

Joined: Sep 2007

Posts: 8,180

Likes: 669

From: Scio, OR

On the passenger side engine compartment fenderwell there is an electric vacuum pump. With the key on, check the pump to see if it is running and how long and often it runs. It should run long enough to pull down a vacuum and then hold it. It sounds like you have a slow vacuum leak.

Also since you mention Max A/C, look for a grey vacuum line in the engine compartment coming out of the heater area and going to a valve on the heater hose (or just to a dummy nipple on the heater core box). If this hose is loose, it will leak off vacuum when the controls are in the Max A/C position.

Jul 24, 2011 | 10:05 AM