BGA9512

My '88 951 is blowing some heat (not full) regardless of the settings. I have verified that the clips are still in place. I adjusted the clip on the baffle linkage so the baffle is closed. The heater control valve seems to operate. It is all the way one way with the engine off and all the other way with the engine running. If the vacuum line is disconnected it reverts back to the engine off position and REALLY throws some major heat into the cabin. As I said, it is not full heat and almost seems to come and go in cycles. The recirc operates, the footwell flap works, the upper flap works, defrost works, the temp control know can turn the heat up, but not off completely.

Based on the symptoms, extensive reading, including Clarks, I am thinking that the heater control valve is allowing hot water into the heater core - either the valve mechanism is not sealing, or because the vacuum supply is being interrupted intermittantly. I plan to stick a manifold vacuum line onto the valve to see if the behavior changes. If it stays the same (some heat) the heater control valve is leaking hot water, if the constant vacuum fixes the problem, it indicates a problem with the temperature control mechanism, probably the servo or control unit itself.

Any suggestions or insight would be appreciated. TIA

Jfrahm

I have had them fail where the valve appears to work but still leaks hot water. I just replace them with an Audi 5000 valve when I have a reason.

hodmandod

Hi

I had this problem. If the clip is fine, look at the vacuum control valves on the heater core. You can see them both, and they control the vacuum. The one on the right is prone to leaks, I guess due to turbo pressure. You can take them off, and check their function by blowing through them, with the heat control up and down. The dash is supposed to come out for this, but you can get at them by removing the glove box assy. You will not be able to reconnect the plug, so cut the old wires and solder on the new ones.

The part # is 944 659 215 02, and in my case, only one was faulty.

Philip

hodmandod

Oh, and also you can check by going into boost, when the heat should come out in boost, but not with regular vacuum.

fbgh2o

Have you verified that the heater valve is operating correctly? I noticed a similar phenomenon recently and then discovered a leaking and malfunctioning heater valve.

BGA9512

I am trying to verify whether the heater control valve is operating correctly. I just switched the vacuum line to the valve so the vacuum is now straight from the manifold and capped the original line through the firewall. During a 10 minute drive the air stayed cool so I think the problem may have been in the vacuum/heat regulating mechanism and not the heater control valve. The vacuum line rubber connector to the firewall was pretty loose and came off when I was changing the vacuum routing, so that may have been the problem. For now at least there is no heat.

eniac

There is something else wrong then.

My heater control valve broke apart years ago and destroyed my clutch in the proccess. I was in a hurry and low on funds since I had to replace the clutch so I temporally bypassed the control valve with a longer hose.

That was at least 6 years ago and I still have found no reason to ever put that valve back in. I have nice warm heat faster in colder outside temps and nice cool A/C still in the summer. My heater works pretty much as it did before. With it on cool I get unheated outside air through my vents, if I turn the temp up it gets warmer to hot just like it did before removing the valve.

ehall

So WTF does the valve actually do then? I've had issues with them in the past. I'd love to bypass that POS.

eniac

Well my A/C might be cooler with the valve but it's plenty cool enough for me without it.

This is a guess as to it's purpose:
I believe it also blocks off coolant to the heater core in severe cold temps so the engine heats up faster then opens when it reaches a certain temp. This makes sense to me since the valve only blocks one hose to the heater core so it stops the flow of coolant but doesn't stop warm coolant from being in the heater core when the car is hot. The other hose is still open to the engine so heat would be transfered through the non moving water in that open pipe. I really do not see any need for that valve at all unless your driving in freezing temperatures.

Before I removed it, it took longer for warm air to come out of the vents on cold mornings. Now as soon as the engine start to produce heat, that goes straight to the heater core and out the vents with the heater on.

It's pretty easy to bypass it, just find a metal pipe from a hardware plumbing section thats the same diameter and put that in place of the valve. If for some reason it doesn't work as I described on my car, then the valve can be thrown back in.

For anyone who's keeping the valve, do yourself, your clutch, and your wallet a favor by moving the valve up near the oil filter like on the S2/968.

ehall

I'm going to give this some thought. Thanks for the info. Living in Florida, cold is pretty much a non-issue. If it's going to be below freezing for many hours, I always run the car for a good heat cycle before putting it to bed, so I may remove mine.

fbgh2o

Crap if I known this five days ago.... I just replaced a leaky valve

Jfrahm

If you want to see what life would be like without a heater valve, just pull the vacuum line and plug it for a few days. I have not tried it in a 944, but in a 928 it's like being in the car with a good-sized radiant heater blazing away. It's a radiator circulating very hot water a few inches away from you. Hot.

-Joel.

BGA9512

Originally Posted by ehall
The heater control valve regulates hot water flow into the heater core (in the dashboard). If you will never want heat, it may be best to replace the two short hoses that connect through the firewall with a U-bend and eliminate water flow into the heater core. Even with the mixing damper closed and recirc on, there is some heat that escapes from the heater core into the vents. It would be better to remove that heat all together by stopping the hot water flow. I figure I will do a bit more testing but being in Georgia, I might switch vacuum lines twice a year if I can't get it fixed.