After accidentally *cough* punching (dont ask) the HVAC unit in my 92 TA, everything works but, the heat will only come out the defrosters nomatter what position its in. It will turn off, and the AC will work, so what the hell did I do? I figured Id ask before I go out in 10" of snow to figure it out.

 

You broke the little vacuum switch that routs vacuum to all the doors that control where the air comes out.

 

...or knocked the vacuum lines off. Pull the control assembly and check it out.

Next time punch the seat!