hvac ??? on Camaro - only A/C blowing

[dream '94Z]

My '94 Z only blows AC out the bottom vents no matter what position the dial is at. It started acting up 2 weeks ago, but switching between settings seemed to fix it, until today. Anybody else heard of this problem? I'm hoping for some hints or advice what I should/could look for before I tear the dash apart.

Thanks.

[Rob B (shoebox)]

Don't tear apart your dash.

An easy way to tell what part of the system may have trouble is to go to the vacuum check valve and test the lines back to the mode selector and to the vacuum canister. If you have a hand held vacuum pump, it would be pretty easy. What you want to do is remove the hoses one at a time and apply vacuum to each and see if it holds. The line to the intake manifold will have to be removed at the manifold and plugged back toward the check valve for you to test the line for leaks. You can test the check valve, too. Often they crack and are the cause of a leak.

If you find a leak on a particular hose, you will have to trace out the cause on that section.