HVAC defrost

[cuda6pak]

Having a few issues with my HVAC setup (manual). For one it will only blow out the defrost and floor vents. I've tested all my check valves with a vacuum pump, and fixed a vacuum leak on one of the plastic lines that goes into the cabin to the HVAC system, but still haven't fixed it. The other weird thing it does is when I'm driving even with the system OFF it blows heat through the defrost/floor vents. It only does this when the engine is running. This is even while cruising around and not under boost. Like I said I've tested all my check valves and scoured everywhere for vacuum leaks and can't seem to find any. Is it time to replace the vacuum switch?

 

[87-WE2]

I had this problem with a previously owned Buick Regal (not a turbo). It turned out I had a vacuum line that had gotten knocked off the carb. I'd re-check all the vacuum lines again.

 

[NarcGN]

had the same problem with mine, turned out the switch behind the control panel was bad. installed this and it was fime afterwards. there is also a T check valve by the firewall under the hood that goes bad.

http://www.nos4gn.com/servlet/the-404/Buick-Grand-National-parts/Detail

 

[NarcGN]

http://www.nos4gn.com/servlet/the-386/Buick-Grand-National-parts/Detail

here is the T valve that goes bad