Todd951968

Any idea what could cause this? I have a 944 Turbo. Both, the heat and AC work normally but when I accelerate and spool up the turbo for a while (like on highway up a long hill especially) very hot air comes out of the vents. I think the AC is still working during this time but it is just overwhelmed by the heat.

After a while things cool down a bit. But, on a hot day in the summer, in a black on black car, it gets really hot.

I've done a search and my car doesn't quite have the same symptoms as others.

I do notice an occasional click of what sounds like a switch or something coming from the glove compartment. I haven't totally coorelated that with the excessive heat issue but it could be related.

Has anyone else had this problem?

VirginiaF1

Is your expansion valve original?
As a precursor, recent refrigerant service completed with proper ounces?

Van

I had that problem when I had a vacuum leak in the HVAC system. When the engine made vacuum (when the throttle body was closed) everything worked. Under WOT or boost, there wouldn't be enough vacuum to keep the heater control valve closed - so hot coolant would flow to the heater core.

Todd951968

Expansion valve is original, I would think. Also, it did have recent A/C service . I assume proper levels but it could be that, too.

A vaccum leak is something to look at too. That sounds exactly like what is happening.

Thanks.

joes

Under hard acceleration the DME turns off the compressor for more power. Alot of time the heater control valve leaks causing heat to go into the heater box but the AC can overcome it but it caused the efficiency to be low and hard to keep up if there is a big load on the system. Make sure your condenser in front of the radiator is clean that can cause efficiency problems when there is a big load or it is really hot. Check vacuum lines and the vacuum reservoir.

Jfrahm

A bad vacuum check valve can cause this sort of thing also. Boost causes a loss of vacuum to the heater valve.

Mangonesailor

What!? Never knew that!

87 944 C

i never knew that either, cause above 3500rpm the engine feels dead compared to no a/c on

V2Rocket

https://rennlist.com/forums/924-931-...ml#post9917692

Joliett

The answer to heat coming out of heater/ac when accelerating uphill is:
A bad vacuum check valve can cause this sort of thing also. Boost causes a loss of vacuum to the heater valve.

The check valve is located coming out of the large brake vacuum chamber, connected to the brake fluid cylinder. You'll see the small rubber vacuum line connected to the small brake check valve. I just removed the check valve, extended the rubber hose, reconnected to the brake chamber, and the system returned to normal operation.

jderimig

I don't think so. Pin29 of the DME just monitors the a/c clutch state to adjust idle. As far as I know. There is no connection from the DME to the a/c clutch relay. Again, as far as I know.

V2Rocket

go out to your car, let it idle, turn on AC, open the hood and twist the throttle to WOT quickly, does the clutch disengage?

thomasmryan

I would look at the vacuum reservoir and check valve for your model. it is there for a purpose. the rubber Ts and elbows harden and the plastic hard lines get brittle with age.

t into the system downstream or hvac side and see if it holds negative pressure with a vacuum gauge. you may have a leak in one of the flapper controls.