Im having quite the odd time here.

03 Monte Carlos have the Vacuum selectors to control the actuators, This car stays on defrost any other settings have a hiss behind the selector in one of the vacant holes of the line bulkhead.

Still the unit stays on defrost regardless. Also blows a little through the vents, Mostly cold on the driver side and hot on the passenger.

Should I find me a new vacuum valve or is there a line MIA?

 

Sounds like a vacuum line may have come off for the HVAC. Most cars have a default setting so that if you lose vacuum or something along those lines, you at least have defrost mode so that you can see come winter I guess.

I've got an 04 SS and those actuators are all electric on mine so I can't speak too much on your issue. Could be you hit a bump or someone kicked off a vacuum line. I'd definitely check for a hose off before buying any parts though.

DH

 

If you have a hiss, it means vacuum is making it to the control head. Sounds like a bad head.