My car has been having problem with ac coming through defroster and not regular dash vents. Also the buttons don't work at all when this is going on. Sometimes during after day of outside air heating up they work perfectly. Mechanic had me buy an ac/heater unit thinking that was the problem, but it didn't work, so hopefully I can get money back. Does anyone have any idea how to fix this? My husband and I are at our wits end! Thank you-Sara
The most common problem if the air doesn't come out of the correct vents is the vacuum check valve located under the passenger side engine black plastic fuel rail cover is bad.
Looks like this.
Since you said the Control Head buttons don't work the vacuum valve is probably not the problem.
There are two modules that make up the C68 auto climate control.
The HVAC Head unit which is the unit with the buttons and LCD.
The HVAC Programmer is the brains of the unit.
The Programmer is bolted to the firewall to the right of the gas pedal.
Not easy to get to but made easier if you remove the drivers seat and seat track.
The GM technician would use a Tech 1 to diagnose which unit is at fault.
The Tech 1 can simulate the HVAC Control Head and send commands to the HVAC Programmer to
verify which unit is at fault.
Below a picture of the HVAC Programmer. You could try reseating the electrical connector and see
if that cures the intermittent problem.
If it doesn't, remove the Programmer and either purchase the Batee capacitor repair kit which includes capacitors for both the HVAC Control head and Programmer. Install the capacitors for the Programmer and see if that corrects the problem.
If you don't have the capability to install the capacitors e-mail him and describe your problem and see if he can repair the Programmer.
Here is the link to his web-site.
At the bottom of the link you can click on a Repair Video describing the Programmer.
BATEE.COM - Rebuilding The 1990-1996 C68 ECC HVAC Controls
Repair video
90-96 Corvette #7 - C68 Electronic Climate Control Repair AC - YouTube
The picture below shows the Programmer and the electrical connector plug you should try and reseat.
