What a nightmare. Where does the vacuum line coming into the interior cabin through the firewall reside? Is it back behind the ducting?

I've got a really bad vacuum leak there (19.5" @ idle, vs 9" with that hooked up - so it's capped right now)

I'm also interested in finding a new HVAC control module. Does GM sell one? Part number?

 

Vadar, if you see this, Could you post the vacuum diagram for the controls? The disc that changes from vent/ac/heater/etc is broken on mine.... so a part number for a new one would be good

Along those lines, is it the Y'd purple one that is supposed to have vacuum from the engine? With a check valve, I take it?

 

Grr... looks like I'll just buy a whole new HVAC control box. Why? Because my old one fell apart, lol. So $37 for a p/n 16066061 via GMPartsDirect.com

Still would like those vacuum routings, though

 

I recently found my check valve and hose lying loose while troubleshooting the vent problem. There was a cap on one of the manifold ports so I hooked the hose up there , with check valve removed, and now everything works. My question is do I need the check valve and where does the other side of the "T" go to ?