"94" C-4 noticed that air only comes from windshield defrost on top of dash. Function buttons light up like they are being used i.e. air conditioning,floor vent, etc. Air will not redirect like it suppose to do. HELP summer heat is roasting us!

 

The first thing I'd check is for a vacuum leak, either under hood or under dash.

 

It will be a vacuum leak mate, and my money is going on the one way valve under the right hand injector cover, it has a T on one side, one goes to the dash vent controller, the other goes to the cruise control servo.


In the pic ubove, youll see the part im refering to just forward of the #6 injector, connected to the top intake manifold vacuum connection, the one under it is connected to the fuel pressure regulator

 

The GM part number for that vacuum check valve Casethecorvetteman is talking about is 10135692.

You should also check the vacuum lines running to and from the cruise control servo on the driver's side below the battery tray.

They can crack/dry rot and cause this problem in the HVAC controller, too.

 

I had the same problem mine was the control valve under the drivers side dash board.1996 was real bad for this. do a quick search I forgot what was the thread. I just fixed mine yesterday..

 

same thing happend to mine, but now my compressor just went out

 

Here I found it. I just trimed the nipples back.
thanks to Digital Disaster ..

Go here or see below.
http://forums.corvetteforum.com/show...=ac+controller









Per Digital Disaster fixed my '96 Grand Sport's HVAC gremlin yesterday, and the problem is the manifold connector on the '96 HVAC controller.

Photo 1 shows the manifold connections on the '96 controller. Notice how the plugs are very soft. They appear to be so soft that they are collapsing under vacuum.


Photos 2 and 3 shows the manifold connectors on a controller I purchased for $40.00 on ebay, unsure of what year it is. Notice that the connectors on this one are hard plastic. Not knowing the compatibility of this controller to my '96, I just removed the manifold connector (photo four) and swapped it into my controller unit. I used a locknut to screw it down.




AC immediately comes from proper vents now, and all other functions work properly.
bvsmith and LannyL81 (above) correctly identified this connection as the culprit. I believe one could clip the soft tips back on the stock controller and also possibly alleviate this problem.

 

Damn, Clay! You sure fixed that problem a hell of a lot faster than I did on mine! My controller's still out being repaired. I did the same thing too. Replaced that stupid speed nut with a regular nut.

 

What I did was open up the hole where the nipples stick through I then pulled the whole thing out of the box (the nipples and conecter) I trimed the ends pluged it back together with the main lines in the harness and used a small wire tie to hold the 2 conections together then I pushed the end with the 2 plugs back into the hole in the box. So basically it is now a connection like a wire plug male/female. It is not bolted to the box it self. It just sits in the box. And it works great..

 

Thanks fellows I'll let you know what I found to be the problem. Time to go to work so I can later play with my toys!