$100 Reward for the answer

[mikeran]

Ok I will paypal anyone $100 that comes up with a definative answer to this problem. Please read everything before recommending me to go to Clarks or telling me I have a busted clip.

Car is always on full heat. Here is what has been done so far.

Replaced heater Valve.
Replaced entire HVAC wireharness.
Via the porsche Service manual tested all 3 sensors.
Tried 3 different all known good controllers.
Tested all 3 servo motors.
Tested the vaccum system.

When the car is cool and Engine power on but without it started, the mixing servo will operate 90% of the time. Start the car and everything will work for a short while, once the car gets hot the servo stops working and it defaults to full heat.

All other functions of the controller still works, the defrost flap will cycle, as will the foot flap. Fan works on all speeds, and A/C will kick in but can't beat full heat.

I am at a total loss of what else to try or check to get this working correctly.

Thanks

[944 Ecology]

Bad control unit.

[mikeran]

tried with 3 different control units all from working cars same effect.

[SolReaver]

Car is possessed. It is channeling the flames of hell to torment your soul throughout eternity. Luckily, it is not as bad as doing a clutch. Solution: Perform exorcism.

But seriously folks: Is there a chance that the wires to the sensors are themselves shorted or broken? This would give the false feedback that can lead to some weird poltergeist doo doo. Check the resistance between sensor groups and individual sensors. You could have some cross talk. Oh, and pick up one of those Archam's razors...they are great for electrical work.

I can tell you some Jaguar Matrix stories that will restore your faith in the paranormal. If it isn't the components it is the connections.

[SolReaver]

Put up a schematic of the circuit involved. If constant heat....the controller has to be thinking it is cold....OR...giving the wrong signal. Any chance you have a connector inverted or backwards?

[SolReaver]

Could you test the sensors from the controller plug?

[mmagus]

I had a similar problem. Full heat once the car was warm. What it actually turned out to be was full heat..all the time, I just felt it when the car got war because thats when the he could be felt. For me here was what it turned out to be.

A stuck flap.

At the rear of the engine about 1/4 of the way down the fire wall is the bo with the flap controls. Coming out of the top is a small plastic tab. That tab has a pull cable attached to it that runs to your heat temp sliders. I took a small woodern dowl and moved the tab. No more heat issues.

Since my car is basically a street legal track car I just left it and bundle up on cold mornings. For you, perhaps replacing the plastic flapper unit, or the pull cable to it will be the trick.

[mikeran]

Sensors were tested via the Controller plug as outlined in the Factory service manual and compared to an extra set that was not in the car all measured same resistance.

Once (Insert problem here) fails the heater valve reverts to fully open. All flaps were reset as per factory calibration guide.

I agree it's possessed or something.

No other electrical issues are present in the car, all grounds have been cleaned, all contacts on the wireharness have been cleaned and checked for continunity.

Please keep the guesses coming, it has to be something stupid and I am out of ideas smart or stupid!

[flash968]

vacuum line to the heater control valve or controller, or bad check valve in the same line, or bad vacuum diaphragm in the heater control valve itself

the vacuum closes the heater control valve, shutting off the heater circuit - when there is a vacuum leak in that circuit, the heat comes on

[mikeran]

Brand new heater valve.
Vaccum is present at the vaccum switch under the dash when the mixing flap works the valve opens properly.

Something random just quits working and when it does the control unit will not control the mixing motor and without that moving the vaccum does not open.

The randomness of this makes me think it's an electrical problem but everything has been replaced and cleaned.

[Dawgz83948]

Have you tried just applying vacuum to the valve itself and seeing if it will stay shut? I don't remember if this system is heat under vacuum or cool under vacuum.

[Guest765]

Originally Posted by mikeran

Ok I will paypal anyone $100 that comes up with a definative answer to this problem. Please read everything before recommending me to go to Clarks or telling me I have a busted clip.

Car is always on full heat. Here is what has been done so far.

Replaced heater Valve.
Replaced entire HVAC wireharness.
Via the porsche Service manual tested all 3 sensors.
Tried 3 different all known good controllers.
Tested all 3 servo motors.
Tested the vaccum system.

When the car is cool and Engine power on but without it started, the mixing servo will operate 90% of the time. Start the car and everything will work for a short while, once the car gets hot the servo stops working and it defaults to full heat.

All other functions of the controller still works, the defrost flap will cycle, as will the foot flap. Fan works on all speeds, and A/C will kick in but can't beat full heat.

I am at a total loss of what else to try or check to get this working correctly.

Thanks

Have you checked the hot and cold resistance of the temp selector switch in the dash? Verify it has a smooth curve and isn't reading different with the car warm.

[mikeran]

fwayfarer - do you know what pins would need to be checked for that? Porsche doesn't publish the specs on the controller unit.

Dawg, it's a brand new valve, but yes it's been checked, default is always to heat on.

[aj951]

Isn't the temp selector part of the controller?

IIRC isn't there a vacuum solenoid under the passenger side dash that controls the vacuum to the heater control valve. You have verified that the heater control valve is good and that valve is opening after the car warms up so maybe the solenoid is failing after warm up. Just a suggestion.

A.J.

[Guest765]

Originally Posted by mikeran

fwayfarer - do you know what pins would need to be checked for that? Porsche doesn't publish the specs on the controller unit.

Dawg, it's a brand new valve, but yes it's been checked, default is always to heat on.

I don't know about the pins but my line of reasoning is that these variable resistance knobs fail in weird ways have you ever had a radio with an old knob that randomly adjusts the volume on its own or with only works for off or full volume? I would imagine this knob would fail in the same manner

[Dawgz83948]

I understand that its a brand new valve, just because it's new doesn't mean its good either. Most mass produced things are not all checked so there is a slight possibility for a defect. Put vacuum to it, close it off and see if the heat comes back, in the mean time that will allow you to check the vacuum put out by the control and verify it is working correctly too.

[billfish]

I have same issue. I solved it by installing a push pull bowden cable to control the heat!!
I still call myself a bush mechanic.

[mikeran]

billfish - I thought about that but I want my A/C to work as well. IF there was a good spec set on the controller I could probably fabricate a manual setup rather than this mixed temp control system.

[flash968]

i had a nick in the vacuum line at the heater control valve - it was fine until it warmed up

[John_AZ]

Here is another possibility....

From "porschecidal_maniac
944online Forum Senior Member"


The second reason that you could have some bleed is that the actual ductwork for the heat vents inside of the dash is a soft plastic flex tube, 2" in diameter which simply routes the hot air from the engine bay through the car from duct to duct and up to the defroster. The hose is made from a very thin (1mm?) plastic and becomes dry rotted and simply breaks at the bends. The air will then not be held back by anything and will find it's way out of the vents, as they are really the only exit points. These are very inexpensive to repair, but a PITA as you need to get physically under the dash which requires removing the driver's seat and the center cluster and the glove box. Also, the plastic flex is not an easy-to-find item so you will need to use intake manifold riser hose which is a laminated cardboard tube with a "slinky" inside to create the flexiness. Any auto store sells it, just make sure you get 2" diameter. The driver side is more prone to need replacement, a single 30" length will do that side and costs around $10.

Good luck. "

Just another idea....

John