95 Camaro, my AC and Heat works but it only come in on the floor and defrost vents. How can I trouble shoot where the vent is stopped to make it start coming out the middle vents. I wear a suit to work and sweat on hot days. To say the least it does not impress the ladies when you walk into work sweating already. Thanks for any information

On the right rear of the engine near or on the firewall you have a vacuum check valve for the HVAC unit. When the air is only blowing on the defrost and the floor, you usually have a vacuum leak somewhere in the system. The most usual place is the vacuum from the engine to the check valve or a broken check valve. Sometimes you can have a leak at the switch. You can usually hear a hissing sound at the location of the leak.

Hi, Thanks for the quick reply.

IT is hard to hear the hissing sound because the engine and the AC is on. I tried turing off/on and then i put my hands up there. What is the best way to check for a vacuum leak other than those two? How would you repair something like that? A simple patch? I'm knew to the HVAC and just dont understand how it really works, it is just plastics tunnels and it has a hole in it?

I use a smoke machine to find vacuum leaks. If you don;t have acess to one, I would start off in the engine checking for the HVAC vacuum line from the engine to the check valve. A lot of times the hose has simply rotted from age. If this is the case it is as simple as replacing the rubber hose. If it's not the hose or the check valve and you can't hear any leaks, you may need to take it to a shop that has a smoke machine to find your leak.

Thanks I'm going to try this and post with my fix. Thanks again.

I had this exact problem on my sons 95 camaro and just fixed it minutes ago. Find the three vacume line located next to the ac unit under the hood at passenger side. one goes to front of car one goes to control switch inside car other runs inside of wire harness and come out at back of motor toward center of intake. this is where the vac come from, mine was pulled out there. reconnected and works fine now. previous owner had plugged, probably because couldnt figure what hooked to it. I used the smoke trick to find disconnected line. I disconnected main line put an extension on it and blew cigar smoke back toward intake smoke came up at back of motor dug around in wires and found vac line. Thank you to the guy with the smoke trick i was having trouble finding where hose came out. :)