My air/heat control system is not working correctly. Air will only blow from the defroster no matter where the switch is placed. The vents will not work. Here is some back ground on where I'm at: Bought the car- heater kinda hissed, when control was switched to air or vent or bi-level, you could hear air moving and then a flop flop flop noise. Like something flapping around in there. Bought new Control Panel Unit- still hissed on heat, would eventually stop though if I moved the switch around from defrost to heat to bi lvl, and back, etc. Had a code 32, replaced EGR valve, no code 32 and heater doesn't hiss anymore and works great. Cool?! still made a flapping noise when switched to air controls though. INstalled new radio, maybe knocked something loose on control panel? Anyways, now the thing is stuck on defroster. I've research through the archives here and read about vaccum motors? Could these be the problem?

The hiss you are hearing is engine vaccum controlling the vent "flaps" diverters. Its perfectly normal. What happens when you move the vent location is the engine vaccum is sucking a diaphragm which is moveing the vent location. You should have some yellow, red, or blue vaccum line or hoses behind the radio. Pull the radio and look in there and see if you knocked one of them lines off. I dont knwo the specifics but that should be enough info you get you were your going. Someone else that knows exactly how it works might chime and give you a better description on the lines and colors.

i went thru the same thing. you have a vaccum line leaking somewhere.
i traced the lines from the controls and found a line that was not plugged up. try this thread.

http://thirdgen.org/techbb2/showthre...uck+on+defrost