Wally95:
default mode for the A/C box when there is a problem is the air just blows out the defroster.
the problem you have is vacuum related or mechanical, most likely vacuum.
the climate control system has a rubber manifold on the back side with numerous hoses coming out of it. We call this manifold the octopus because it kind of looks like one when you take it out.
vacuum comes from the engine bay. Full manifold vacuum from the intake manifold goes to the vacuum canister on the passenger side of the engine bay.
a hose from the canister then goes into the cabin of the car through the firewall.
that is the main vacuum line that feeds into the octopus and through that all the vacuum motors function when selected.
many times something falls apart in the system and gets blown into the control system which clogs up the mechanical.
you can try using a hand vacuum pump to test all the vacuum motors one at a time and make sure they work and do not leak. this will move all the flappers internally and make sure there are no mechanical problems.
if the motors and flappers all function then the issue is inside the controls where the levers/sliders are. you will most likely need to remove that control panel and try to blow out the clog, sometimes you cannot and the control panel will need to be replaced.
there are other issues that should be looked at the same time. the vacuum canister should be tested there is a reed valve inside that must only allow vacuum to flow one way. you can test the reed valve by blowing and sucking air into and out of the canister if air only moves one way then the reed valve is good if you can move air both ways then the canister must be replaced.
the heater core control valve should be inspected and tested for operation, they rot out over time and need to be replaced every couple of years.
so test the motors one at a time using a hand pump. make sure everything is free and working without leaks. then take apart the control panel and remove the octopus blow everything out with compressed air, inspect for cracked dry rotted rubber hoses and replace as needed.
blow out the controls and you can try hand testing the manifold with the hand pump. the hoses are color coded. Black is the vacuum input.
http://s1031.photobucket.com/user/72hcode/library/Heater%20Box%20AC?sort=2&page=1
