I have a 96' Z28 model and my A/C will blow through the bottom vents but not the top. Can somebody help me out and tell me what the valve is or what's the problem and also how to fix it?

 

Take a look under the hood near the A/C evaporator box. I know on my 95 there is a little plastic check valve there that the small hard plastic lines connect to. Three of them. The little plastic check valve snaps into a groove I. The a/c evaporator box. Heat destroys the valve over time, and it just falls apart. I'd swear that when mine was broken it defaulted all of the air to the dash vent, but I could be mistaken. Might be as simple as that. I was able to find a replacement on eBay for about 4 bucks all day long. Good luck

 

Like the other responder stated, check for a vacuum leak at either the check valve or the vacuum tank itself. When control vacuum is lost, the system defaults to floor and defrost vents only. The check valve is near the A/C pipe connections at the firewall and the tank is in a hidden cavity below the battery and ahead of the right front wheel.

 

Do a search on here for shoebox look at his signature click on " how to"
there is something in there about " restoring airflow to my vents "
I was cleaning my intake with a wire brush and disconnected a small air line that plugs in
ontop of the intake. The air line/vacuum line controls your airflow to your vents

 

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