I have a problem with the "button" (its not really a button but i dont know how to say it in englidh) the controlls where you want to hav the air in the coupe. Regardless of wich mode I turn the "button", all air comes on the front window. The only mode that works is off mode, the rest just blows on the window. What can be causing this, and does anyone have simular problems? The car is a -93 Z28

 

I assume that you are talking about the defrost. Sounds like the mechanism that changes the flow has broken. Not sure how to fix it though

 

ive located the problem to the "hvac check vaccum valve", wich were broken. I replaced it with a T cross, and it seems to work! Should i put a back valve on the hose or can I run with this setup?