Hi my 89 Turbo blows hot air through the heater vents under hard acceleration even when the ac is on. Any ideas......? With thanks Gary

 

so the heater is on all the time?

 

Search the list and you will find the only inexpensive 944 fix that exists – your white plastic heater control rod clip is broken - $2.

 

The heater and ac seem to work fine (hot when set to hot and cold when set to cold) however when it is set to the cold setting, regardless if the ac is on or not it will suddenly expel vast amounts of hot air through the vents as if the heater control has been turned to hot when I accelerate hard. Then it will return to cold when I ease of. Will this white clip cure the problem. With much thanks Gary

 

I experienced the same issue yesterday! Thought it was a vacuum issue (assumed the controls had a stuck door etc).

Now I only have to figure out why the car is stalling at idle sometimes but then starts and runs perfect the next 20 times I start it!

 

Yes, more then likely, the little clip is your problem...

 

Check your vacuum lines to the vacuum accumulator. That’s the black plastic thingy near the battery. It stores vacuum for the HVAC controls for use when you run wide open throttle for a while (no engine vacuum). There should be a check valve in the system somewhere so that the vacuum does not get lost back to the intake manifold. Either you check valve is shot or you have a vacuum leak on the HVAC control side of the vacuum system.

 

The check valve should be blue, near the center of the firewall above the intake manifold, it T's off the big brake booster vacuum line.

 

Sounds like a vacuum leak, had to deal with that a few weeks ago. Check the vac lines to the heater valve and the vac lines that go into the firewall.

 

+1 on the check valve in the line to accumulator. If you have messed with the vac lines at the rear of the intake, check the line going to the heater control valve right above the S&R sensors. It should be hooked to a hard plastic line coming thru the firewall near the AC lines. Its probably hooked correctly, but with a bad check valve, it gets suck, then blow, and gets confused about sending hot coolant to the heater core.

 

Check the heater bypass control valve is operating. Had a similar problem and the diaphram failed and valve failed in the open position, causing coolant to flow through to the heater core. Did you recently have the cooling system flushed or coolant replaced? It could be air still in the cooling system and the hot air is collecting in the heater core under hard acceleration; re-bleed the cooling system.