Hey guys, here is a wierd one for you. Whenever I turn on my vents or A/C, the vents on the top of the dash don't work. The Defroster works, the bottom vents work, but the ones on the top don't, not even a little bit of air. It doesn't matter what setting the vent is on, no air. I would assume that there is a flap or something like that stuck covering the vents but I don't have a clue where to start. ANyone have any ideas? THanks for the help.

Sean

 

It's a common problem. Here is something I already have written up:

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 (like a Mityvac), 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 it cracks and is 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.

Most of the time, it is the check valve that is broken/cracked.

 

I had the same problem a few months back and Shoebox was right on the money then. Go to the chevy dealer and get yourself a new check valve. Take that part number with you, it will make things much easier.

 

Just to throw my .02 in, I had the same problem. I looked at the vacuum check valve in shoebox's diagram and compared it to mine, and my $6.00 valve was definitely the culprit. Popped a new one in (took about 30 seconds) and everything was golden. That's more than likely your problem too.

 

That was it, the check valve was broken. THanks a lot guys!

Sean