nherbert

It might be simple, but before I tear into the dash I figured I'd hit you guys up. When I put the switch to front vents on the heat control module, I get no airflow, only floor and defrost gets airflow through various positions on module. From what I've been told, GM ran vacuum lines which control this particular part of the system. I've pulled the module out of the dash and now i'm just tinkering/troubleshooting. My question, is it just simpler to replace the control module with a new one, or can I actually troubleshoot the system; loose connection, ground, etc. Any help would be greatly appreciated, until then, I have a case of beer, a clean working garage, and a whole weekend to work on this. Cheers and have a good weekend.

Spartan7

iTrader: (7)

Yes, the vents are indeed controlled by engine vacuum. However, narrowing down your problem could be very difficult. It could be a stuck door, bad vacuum diaphragm, bad vacuum line, or a bad switch on the HVAC controls. Most of which require tearing apart the dash to get to. You can see the vacuum lines and diaphragms that control all the doors here:

wssix99

iTrader: (5)

Try a search. Lots of threads on this.

If all control positions don't change the vents, you probably have a master leak in the line coming from the engine compartment. (You may check the lines and fitting in the engine compartment first.) You can also get a vacuum testing tool from the auto parts store to test how the lines hold a vacuum if it gets tricky.

nherbert

Thanks guys, that's the info I was lookin for to get me started. I'll start troubleshooting based on these suggestions.