Air only comes out of the defrost vents.

[nickvargo213]

Gen 1. The control for AC, defrost and vent selection seems to be malfunctioning. It will turn on the blower motor, but not the AC. Also all the air comes out of the defrost vents on the top of the dash.
The hot cold and the blower speed controls are working properly. I've taken a look, and the vac. lines are connected. I haven't torn into it yet. Am I on the right track with this?
Has anyone else had this issue?

 

[Welfare racing]

I have air that keeps blowing thru the vents when it's on other settings, like there is,a bad seal somewhere (cool air on a cool day) as it's heating the defrost and floor on a 97 rt10