Air will blow on the bottom and on the to dash defrost vents but not on the front vents? What should I check?

 

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. Sometimes 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.

 

I was having the exact same problem. Thanks again shoebox for the diagram. Turns out the top nipple was busted off of the valve. It was like 5 bucks at a local dealer. Took 2 min to switch, and solved the problem perfectly.

 

Yeah that'd be your vacuum check valve...

 

One more Hell Yeah to Shoebox, I hope his posts have helped everyone else as many times as they've helped me.