Hey guys, my upper dash vents have stopped blowing, the lower (under dash) vents still work just fine. The problem was intermittent at first and now they have not blown air for over 3 days. I dont have a manual for the car so I dont know how the vents work, is it a door, vacuum actuated, where is it? If any one can help me fix this problem I would be very appreciateive, its 90+ degrees around here and this is killing me! Also, the upper vents do not blow regardless of the setting (ac, vent, heat) and the defrost works.

 

You have a leak in the line that provides vacuum for the controls. A lot of times, the check valve breaks.

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.

 

right next to the pcm there shpould be some vac lines 3 of them one goes to the vents the other to intake and the other to vac canister and they are connedted by a check valve see if there is a leak threr

 

This sounds like a vacuum leak to the system that actuates the vents. Theres a check valve located directly behind the passenger front wheelwell that controls this. Shoebox's site has detailed pictures on this that should really be able to help you figure this out, good luck.

 

Damn you guys posted before I even got done typing, awesome.

 

I will take a look at it after work, assuming teh lines are ok, does anyone have the part number for the check valve, something I can pick up at the local parts store? Thanks guys, I woulnt have to sweat it out much longer.

I am thinking it is the check valve. I was looking at the diagram and the vacuum line that comes off the check valve runs to the selector. If that line had a leak, then wouldnt the bottom vents not blow as well? It does appear that there are doors on that diagram as well, is that a possibility or should I only be looking at the vacuum lines?

 

i had to get mine from gm you can use a t-connectoe temp it will just not stay at the setting when you shut it down the defroster will comone when youm satrt up and then will transfer to the vents after vacumm builds

 

Part numbers are on the link that was in my post.

When there is no vacuum, the vents default to the floor/defrost because of a spring in one of the vacuum actuators.

 

Thanks Shoebox

 

ShoeBox. You are THE MAN! Thank you so much for all the effort that you've put into your site and helping others. I just stumbled upon this thread, went outside and 3 minutes later my problem was solved. This is the 3rd time you've helped me out without knowing it. THANKS!!!
And also thanks to all other who participate in this message board. Without your questions, help, and messages I'd be a much poorer man!