Here is the low down. Heater works, so does A/c, but the vents are being stupid.
I plugged my heater valve switch vacuum line but for the longest time my vent and heater selection opens only the defroster vents.
Nothing comes out of the normal vents or the floor vents! Anybody have some sugestions as to what might be wrong. The vacuum lines are all attached at the back of the hvac unit.

 

J,

Either you are not getting vacuum to the ported vacuum switch on the HVAC control cluster, or the vacuum switch is leaking. Thsi is fairly common on older cars, since teh switch is actually two pieces of plastic that rotate to change ports. These two pieces are sealed by a layer of silicone grease. After time, the grease becomes hard, dried, contaminated, and fails to seal the switch ports. You'll need to remove and clean teh two havles, then apply a fresh layer of silicone grease (Permatex dielectric silicone works fine for this).

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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
Adobe Acrobat Reader

 

Thanks, I think that is my problem. I replaced the unit after my original was destroyed after the break in (totalled car rom inside). I can hear the leak, it's pretty loud. I hate removing my dash, especially when it's winter and I have no warm place to work on it .

 

It appears that I am in the same boat. For a while now my heater has been hissing when I switch to the heat option, not on anything else though. Lately it has been hissing longer and longer too. Sounds like I need to tear my dash apart in the middle of winter to find the problem.
Joy...
Randy

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1986 Camaro SC
White
LG4 with Edelbrock Performer intake