1990 corvette HVAC issue
Thread Starter
1st Gear
Joined: May 2025
Posts: 1
Likes: 0
1990 corvette HVAC issue
Hi, I have a 1990 Corvette with automatic climate control opt C68. When the car is in the accessory position, the HVAC controls work perfectly, allowing me to adjust the temperature and fan speed without any issues. However, as soon as I start the car, the system defaults to 75 degrees, and I lose control of all functions except for the rear defogger. The car has a rebuilt programmer and a new control head. I’ve confirmed a constant 12 volts at pins 1 and 2, along with a steady 8-volt reference. Both positive lines and the ground to the HVAC control head have been load-tested. There is no error codes displayed on the screen. It’s strange that everything works fine in the accessory position but stops functioning properly once the engine is running. Has anyone encountered this issue? Thanks!
Drifting
Joined: Feb 2016
Posts: 1,384
Likes: 339
From: Simi Valley CA
Just a guess, but there’s a vacuum line going through the firewall by the brake booster. It is a typical vacuum leak as that hose is made from soft rubber that gets brittle. That hose goes to the control unit to the right of the gas pedal.
