My 87 944 turbo at times does not blow hot air even though the engine is warm and there is no air in the cooling system. It DOES blow hot air if the defroster is selected, but otherwise the heat is barely warm.

I would appreciate any help into this problem.
Thanks
Ahmet

 

Have you checked the vaccum line that goes to the heater valve? It "tees" off and one end goes over to a post down low kind of behind the exhaust manifold and another connection goes through the firewall into the battery box to the vaccum booster or storage unit or whatever that black can is. Check for leaks and I'll bet it'll work.

 

Are you actually cold or does it just seem that the heater isn't working? Remember that the heating system is thermostatically controlled. What this means is that it initially runs full blast until the interior reaches the set point. Then it seeks to maintain that temperature. When that happens, it seems like cool air is coming from the vents. Even 72o air seems quite cool to touch. The key is if it's cold outside but you are maintaining a comfortable interior. If it is malfunctioning, another failure point would be the temperature sensor behind the dash if it has become blocked or quit. But first make sure it is a problem and not just because it is different. I know I was used to heaters putting out warm air all the time and I wondered about the Porsche's until I realized it was just normal since I was still warm enough. I still miss a little blast of warm air once in a while (now I just kick on the defroster for a minute or so to warm up the hands.)

 

I can't help you with the Porsche, however, my mercedes does the same thing. Reason being it mixes the air temperature from hot and cold air. By the time it comes out the vents, it's at the correct temperature. That's just how it is on my car though. I feel like it's not heating very well at times either, but on defrost it heats one hell of a lot.

 

The vacuum to the heater control valve is fine (and the valve functions correctly as well). Also a note to this is that if the heater valve did not function correctly, there would not be much heat avail. at any time. Defrost produces A LOT of heat. Turning the temp selector to full hot does very little (and it's intermittent).

I know that the inside temp is supposed to be regulated but I'm talking about barely warm air when it's around 45 degrees outside. I have never ran into this issue on any of the 944s I've owned or worked on. I'm leaning on the possibility of interior temp sensor, but is there some way to test this before jumping into the replacement?

Help is much appreciated guys.
Ahmet

 

Right you are - okay that makes sense. Check the inside temperature sensor. I'll check the manuals tomorrow to see if there are specific voltage readings you should get at particular temperatures for testing purposes (unless someone beats me to it). . .

 

Thanks a bunch, also please let me know if you run across anything else (overall system testing procedures, other symptoms, etc.).
Ahmet

 

Bump!
Ahmet

 

Two things have to happen for heat to be really hot, the heater control valve must open and the flap in the dash must move from the evaporator core to the heater core.

I believe the evap core flap is controlled by the motor that the "heater clip" is hooked to. Is it moving? Since it works on defrost, I would suspect a bad control unit. Swap in Dooberbrains next time you're near his car.

 

Good call. His car's parked next to mine and there's one more at the shop, shouldn't be a problem. I'll do it in the next few days and report back.
Ahmet