Heater Problem, Help!!
 

Hello, the problem I am having with my 1986 Porsche 944 is that when I turn the heater knob to cold the air does not always go cold.
Sometimes the air is just blazing hot. When it is cold it then changes to hot every once in a while. It will stay hot all the time most of the time, but I can not get it to stay cold. Any suggestions would be greatly appreciated, spring is coming up soon, and I'm going to roast if I can't fix this.

I had a problem with a 928 where heat wouldnt shut off. Spent a fortune on it. It turned out to be a sticky flap door. I didn't do the work. Cant tell you anymore.

I know this sounds too simple, but have you checked the heater control valve? The cable could be binding, slipping, or possibly broken. Or there could be gunk on the inside of the valve, keeping it from fully closing.

Two important things to check are the integrity of the vacuum circuits that control the heater valve. The valve is CLOSED by vacuum, a leak in the circuit will allow the heater valve to remain open constantly. One of the small plastic control lines could easily slip out of the rubber hose connectors. If the hot air blast comes on during open throttle (low vacuum) then won't go off, suspect a vacuum leak.
Second thing to check is the temp. sampling system. On the dash next to the clock is a small (1" dia) grill that is connected behind the dash to a 5/8"hose which leads to a small blower. The blower pulls cabin air over a temp. sensor to tell the system whether to send heat to the cabin or not. Chances are the hose is long gone, or slipped off it's connection at either end when someone pulled the glovebox out. Must remove the glovebox to access this hose and blower. Be sure the little solid state sensor is clean. It looks like like a small electronics capacitor held in the center of the air stream as it enters the little blower under the dash. Also be sure the little blower works when the heater blower is running. Be careful when removing the glove box. The light connections can easily ground out and blow a fuse.
Happy Motoring.

Thanks for the help everyone, I solved the problem!!!

Rich

So, what was the problem, and how'd you solve it?!?

The plastic clip was broken on one side, so it would grab sometimes and sometimes it wouldn't. It didn't seem like the infamous plastic clip problem but it was. Thanks for all the help everyone.

Rich