Porsche Enthusiasts Club Forum

1986 944 2.5 - Oval dash with climate control.

Can't get any warm or hot air from the heater whatsoever.
I've fitted a new one way valve (black & blue colour) that sits near the brake servo unit. I couldn't blow through it, should I be able to?......It's brand new from Porsche. I've got the black piece facing the engine and the blue part facing the bulkhead.

The heater control valve that sits under the bonnet at the back of the engine only opens when I press the dash mounted air recirculation switch in. The valve doesn't open when I turn the climate control knob to the right / fully on. Should the heater control valve open when the climate control knob is turned to the right?

No warm or hot air either from the de-mist button, just cold air again!

When I move the slider controls to the left & right I can feel the air with my hand in the footwell coming on and shuting off, same on the dash vents. So the plastic clips that usually break don't seem to have on mine.

Any advice most appreciated.

Cheers,
Kev.

If the heater valve is only moving when the defrost button is used, the problem may be with the cabin temperature sensor (as yours in a climate control one, rather than the basic version), or the main circuit board in the heater control unit.

The one way valve should allow you to suck air through it at the black side, and not blow through that side.

The servo check valve should allow you to suck through the vacuum hose side, but not blow through it.

Many thanks for reply above.
Blue & black one way valve works fine, l can suck air through it from black side.

Under bonnet vacuum heater control valve only opens when I press in the air recirculation button. No hot air at all from de-mist button, just loads of cold air.

Whereabouts is the under dash interior heat sensor? .....passenger side??....and what does it look like?
I'll attach photo of my heater control panel tomorrow so we both know my particular unit

Thanks for any further help. Posted this from my mobile so hope it comes across ok....

Photo of heater control unit......air recirculation button far right. De-mist button far left.

Took the car out for a run today. After covering about 4 miles I reached down above my left foot where the two pipes are leading to the heater matrix through the bulkhead. Both were warm/hot. So water is reaching & exiting the heater matrix - good!

I popped open the bonnet, the lever on the vacuum operated heater control valve at the back of the engine had not moved into the unit. I pushed the dash mounted air recirculation button and the lever went into the valve. Hot water was still flowing in and out of matrix.

I still couldn't get any warm / hot air out of the dash vents into the cabin no matter how far round I set the temp control knob or moved the sliders over to the far right. No hot air either from the de-mist button.

It seems I need to find the under dash temp sensor........if only I knew whereabouts it was and what it looked like!?

I seem to be so near yet so far away from getting some heat into the inside of the car.....lol

The round shaped slits in the dash next to the ciggy lighter - I removed the rubber tube that fits behind it where it fits onto a little motor that comes on with the ignition. This seems all A-Ok, the little motor spins around with the ignition on and slows down to half speed when I push in the air recirculation button. I re-fitted rubber tube plus glove box.

jmgarage.........HELP! Please.......

I don't have first-hand experience of the climate control system, but looking at the circuit diagram I would suggest that the little motor 'thingy' that has a hose to the slots in the dash is actually the interior temp sensor. Seems that the fan runs and pulls cabin air across a resistive element that varies with temp, this is then measured by the control unit. See circuit below:



Hope that helps..

Wow! many thanks for the above.

I suppose my next step would be to replace the little motor and plastic black box that it sits in?

I'll get onto my local Porsche chap and find availability & price .......wouldn't be keen on a second hand one.

Cheers,
Kev.

There is a flap in the heater blower assembly which switches airflow from going through the heater matrix or bypassing it.

If when you move the knob from cold to hot inside the car, the rod in the valve under the bonnet is moving, your temp sensor is probably ok and it could be the plastic rod that actuates the above flap is broken (quite common)

If you look up between your glove box and the side of the heater control unit, there should be a white plastic rod, about two inches long, which has an actuator on one end and the other end attaches to a metal arm which moves the flap. Often the end of this plastic rod breaks, the plastic rod swings round and jams, which leaves the rod/flap in the cold or hot position, so either constantly putting air through the matrix, or constantly bypassing it.

Hi Kev, as JMG states, it could be this device, or the control unit. It would be a shame to get a replacement sensor only to find it wasn't that .

So, it would be good to test the sensor first to see if it is operating. Now, I don't know the typical resistance range of this device, but a simple check would be to remove it and put a multimeter across pins 2 and 4 and see what you get. If it is either 0 ohms or infinite then you know it is bad. If you get a stable reading I would suggest you pass some warm air into the device (hair dryer on cool?) and check what happens to the reading (it will either go up or down). If it doesn't, then again it might be faulty. If it does respond, then let it cool back to the first reading and try the test a couple of times. If they all appear about the same I would think it is operating OK.

If it is OK, then the next thing would be the control unit ....this is not really repairable as I have hunted high and low for a circuit diagram and gotten nowhere (even the simpler standard heater one!). If you know someone with a spare known good one, here would be a good time for a substitution test.

Hopefully, it will be the sensor (but they are probably quite expensive!).. good luck!

Just another thought..there are a couple of other sensors in the heater box itself, however I cannot tell from the circuit diagram which ones are used for the climate control rather than the AC version..if anyone else has any experience with this problem some further advice would be good! However, I understand that climate control is rather a rarer beast than the standard heater.

......just seen JMGs latest post too..yes, you need to check that rod. Generally it fails so you get hot all the time, but it could be a culprit. see Clarks Garage for a full procedure and photos, etc on this issue, it also gives you a pretty good idea on how the air circulates around the heater unit and which relay operates what flap, etc.

Many thanks for replies above. Plenty of food for thought.

On turning temp knob inside car the heater control valve under bonnet doesn't move / open.

I'm aware of plastic clip & rod assembly. I'm sure mine is all in working order.

Busy week coming up so it'll be next weekend before I get another chance to fiddle about with all of this.

Hi again, just had another quick trawl around for info and came across this..I can't verify its accuracy, but it might help if you decide to test the heat sensor:

"Check the three NTC resistors that measure the outside, inside and mixed air temperatures.

The outside NTC is located under the hood under the plastic cover at the right side of the car just in front of the fresh air inlet. Should measure 22 Kohm at 20 degrees Celsius.

The inside NTC is a little more difficult to get to. It is located behind the glovebox. There is a small motor/fan unit that sucks air from the passenger compartment. (Next to the cigarette lighter is the intake) should measure 10Kohm. The NTC easily becomes dirty with dust, cleaning might help.

The mixed air NTC is located behind the fresh air outlet in the middle of the dash. Remove the plastic part (around the instruments and the air vents) and you see the NTC. This one also should measure 10Kohms.

The NTC's can be tested by holding one between your fingers, the resistance should drop. With some patience they can be replaced by one you can buy at an electronics store. I did, and the NTC's work just fine for over a year now."

I think some of these sensors apply to a full AC system, but not entirely sure, but the test for the interior one looks sound. NTC stands for Negative Temperature Coefficient - in other words the resistance decreases with increasing temperature....so it's a Thermistor.

With a multimeter you should now be able to verify the sensor operation..have fun!

Update: I have HEAT inside the car!

Thanks for your replies above

Hopefully I've sussed out why I was only getting constant cold air from my heater.
The little motor that works when you turn the temp knob had partly seized. It fits on the side of the heater unit and can be easily removed once glovebox is taken out. I removed it, gave it a clean and a squirt of WD40 and it seems to be working all A-Ok now.

The rods that fit into the little white clips were all seated ok, so that was all fine.

Don't think I need to worry about thermistors / heat sensors at the present time.

Fingers crossed I can get heat from the heater all of the time now. First time it's worked for over a year!

This link is very useful.......


http://www.clarks-garage.com/shop-manual/hvac-01.htm


Cheers,
Kev.

Hi Kev, good to hear it is sorted, especially in this weather!