The heat in my car is only coming from the defrost vents. I know that the main cause of this is because of a broken vacuum line somewhere. So I put a vacuum gauge on the hard vacuum line that comes through the firewall and applied vacuum to it while holding my finger over the vacuum connector that goes to the heater controls. If there is no vacuum leak at this vacuum line then where would it be?

 

The switch itself is often the culprit. Stick you ear to the HVAC and listen. Should you hear the tell-tale hiss, I "believe" this is what you'll need: Valve Vac Sel GM part # 16032395.

JamesC

 

Well I changed out my heater controls with another one that i had and it is still doing the same thing. Any other ideas?

 

The heater controls you put in may be bad too.

 

Does the hard vacuum line from the a/c harness have to go to a check valve or can it be hooked right up to a direct vacuum source?

 

It ended up being the part that James mentioned. Thanks for the help.