In my car, no matter where I set the heater control the darn thing only blows out the defroster vents. The vacuum cans that work the doors inside the heater unit are not getting vacuum, where is the main vacuum source, and what else should I be looking for?
Thanks.

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89 Formula, Maui Blue,355 TPI(used to be TBI) Auto, TES, 3" dynomax Hi-Flow cat, 3"Flowmaster single in, single out cat back. B&M shift kit, afpr.
89 Formula, Black, with really bad paint, 305 TPI Auto, t-tops bone stock (so far)

 

John,

The vacuum source is a 1/8" hose fitted into the plenum vacuum port near the FPR vacuum line.

Any other significant hose leaks in the passenger compartment can do the same thing, causing all air doors to dump to the default positions (out the defrosters).

If the line is intact, you might have a problem with the rotary vacumm valve in the heater control console itself. After several years, the silicone grease on the ported valve halves tends to dry out and get displaced. If you find this to be the case, clean off all the grease from the valve halves. Apply a fresh layer of dielectric silicone grease (Permatex item) to both halves and reassemble it. This usually seals the device for another ten years or so.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

EDIT: Doh!! Vader beat me by a minute!!

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

[This message has been edited by Engineboy (edited December 16, 2000).]