Do I need a new Temperature Control Unit?
 

Trying to fix the 'heat always on' problem on my 86 944 n/a. The plastic clips under the dash are ok, I replaced the heater control valve, so the only thing I can think of now is the temperature control unit? How much do they cost and where can I buy them?? This happened several years ago and i've just had the heater valve tied off, but now I want to sell the car and have the heat working properly. I remember the night the heat broke, it seemed to happen right after I drove down an extremely rough road that was under construction. In case that helps with the diagnosis...

Thanks

Kind of hard to point to one thing. Check out Clark's garage. com at the link below.

944 HVAC Operation and Malfunctions

Cheers,
Larry

Did you check if the heater valve you tied off is getting a vacuum signal. Check the vacuum hose maybe it just came loose from the solenoid valve coming from the firewall while driving down the rough road.

Have tried clarks-garage, and I had a shop do the heater valve and at the time they also noted the car had zero vaccum leaks.

I had the same problem heat on constantly, clips were fine, heater control valve new. I even changed the HVAc control unit and still had the same problems. Spent about 2 days of trouble shooting and finally found the wiring harness was bad, changed it and everything worked fine again.

Check to see that the controller is moving the correct control servos.
Top slider controls the rear most servo, bottom slider controls the front most servo
The temp control controls the middle servo, the middle servo controls the vaccum servos on the other side behind the glove box. If the vaccum servo doesn't get any power it cannot shut the heater control valve.