Heater Control Valve? Maybe?
 

Can someone tell me some possible symptoms of a failing heater control valve. I have a 78' 924, which recently had a head gasket replacement, new vacuum lines, timing belt and other small projects.

I have had the car about 6 months, 4 of which it was parked for the winter. Now I am starting to work through some of it's issues. The blower fan does work and I get heat all of the time through the foot vents or the window defrost vents, but I get cool air (no heat) from the vents in the dash. I find this a little strange since it all comes from the same place or at least I thought so.

I am wondering if the heater control valve may be causing such a problem. Maybe it is stuck open? From what I have read, it is a part that commonly wears out.

Any thoughts would be appreciated.

Constant heat is an indication of a broken heater valve.

Happened to me in my '85 944. Changed the valve and problem was solved.

Can it be that the vents on your dash are for the A/C? That woud explain not getting hot air through them.

I believe A/C air comes from the evaporator. The hot air comes from the underdash heater system radiator. They are different.

If it is the same as an early 944, it is a pretty cheesy setup, so it could be the control wire not being properly connected or routed, follow and see where it leads.

Heater valve would only cause the heat never to blow cold. There is a flap for the dash vents that changes between the evaporator case and the heater core case. Some part of that system is not working. It should be vacuum actuated. There are several plastic pieces hat can break too. Good luck. Without some skill you just dove into one of your most complicated systems.

I have not had the car all that long and this problem has been a back burner sort of problem. The previous owner told me that the A/C did not work. I realize that that could be any number of problems.

I have verified that the vacuum valves for the a/c are working. I have replaced all of the vacuum lines and they now move when they did not before. The vacuum tank for the a/c was disconnected when I got the car.

I am not so concerned if the a/c does not work but it would be nice to not have heat blowing everytime I run the fan. I only get heat from either the foot vents or the defrost vents.

I guess it is time to spend some quality time with my head up under the dash trying to figure out how it is suppose to work and what is causing the problem. The heater control valve does sound like a good place to start possibly.

Again. Heater control valve is not your problem. Heater control valve symptoms. Only hot air through ALL vents no matter where the heat slider is. You are getting a mix. To test heater control valve turn ac on and see if you still get heat from any vents. If so the valve is not closing.

Easier and more difinitive test. Put vacuum pump on control valve. Pump closed. If it moves and stays closed its good. Unless its broken inside which you could test using both tests combined.

Here's a complete tutorial regarding the heater control valve 944 Foot To The Floor: How to repair heater control valve on a Porsche 944 (Square Dash Model) Hope that helps