Porsche Enthusiasts Club Forum

When I first got my 944, the heater often stuck on hot. Now though, it is generally giving out cold air regardless of what the temperature knob is moved to. Every once in a while it will give out hot air, but I want to be able to control it AND guarantee hot air availability through the winter. The button to force air to the windscreen works and forces hot air, so the system seems to be working to some extent.

Is this a problem with the temperature knob? There's no clicking sound from it when moving from cold to hot (and vice versa).

My car is a 1986 oval dash 2.5 model.

Thanks in advance for any help

It is hard to say what is wrong but generally a heater being stuck on hot is down to the vacuum pipework (for the heater) being awry (with no vacuum the system fails to fully hot). I would check the connections everywhere first (and the vacuum diaphragm itself on the heater pipe (this can be tested with a syringe or by simply seeing that it moves when the temperature control is moved).

I would also check the clip by the glovebox. It going cold though is throwing me off. Has the cooling system been worked on lately?

I have a spare heater control panel if you want to borrow to test.
Send me your details if you wish.

Nick

Excellent advice so far.

The clip by the glovebox is so common, I have even had customers who had owned their 944 for years and presumed that the cars had really idiotic heaters until I pointed out their clip needed replacing following a test drive.

The vacuum side does indeed need to be right, with a good check valve (the blue and black one behind the engine) and sometimes has been fitted by someone in the past the wrong way round (Black on the engine side, blue on the heater side of the circuit)

Lastly the heater valve in the engine bay is vacuum operated and can fail, often either giving permanently hot or permanently cold air.

We did have one customer who had all of these fail, and after it all still had issues, and it turned out he also had a bad PCB in the heater controls, which was a real pain to find a replacement for, but I think that Porschapart refurbish them.

I've literally just now replaced (well, glued for now) the plastic clip on the linkage for heater control on my 944.

Mine would be fully hot unless you had it turned fully cold.

Hoping this has sorted my issues, but have also heard of the other problems mentioned above.

If you do have a broken clip, I believe the part number is 944.572.314.00 - I have glued mine for now and it seems OK, but will order a new clip anyway.

Incidentally mine looks like it may have failed due to the linkage getting caught in amongst the cable looms from the clock & fag lighter.

I suspect they have been removed previously and have been put back with incorrect cable routing. I have pulled them out of the way which allows the linkage to move freely now, although as they are the clock wiring still moves slightly with the linkage.

Should there be a cover over the linkage/servo unit? If not, does anyone know or have pictures of how the cabling should be routed?

I have heat on all the time . Clip/rod in passenger footwell is ok so must be vacuum pipework . Can someone give me an idea of which pipes I should be looking at?

Bump

Getting back to sort this issue now that spring is here

The vent hole next to the ciggie lighter also determines cabin temps - it runs all the time on a little drive motor under the glove box area - if the hose is not connected, it my give back spurious info back to the heater matrix ensemble... The heater control knob doesn't 'click' when turned - more like a rheostat dial. As you are getting power defrost - removing the heater control module maybe an idea and to dust out the connections etc. Simple job and the wiring is block connected - just be careful with the facia panel piece - it can brittle.

Dave
CT

I had a look at it yesterday evening . looks like its the heater control valve . i manually pushed it across and the air from the vents was cooler . I have ordered a replacement valve . Hopefully its a case of the valve not operating properly as opposed to the vacuum feed not been right in some way.

ok . so fitted the new heater valve and all seemed good . however i appear to have misplaced the hose which clips on to the the white clip outlined in the picture . any ideas what this line is ? I need to find it (i assume its dangling freely between engine and bulkhead and make sure its connected)

The heating controls worked fine for a day and now arent working again . i assume as a consequence of this hose.

you can follow most of them, it all starts from the vac on the brake booster, that white clip on my car holds the connection for the O2 sensor??

The heater valve is working but the controls are a little erratic . More investigations await

Back to hot all the time now

Mine failed too. Tried all the easy stuff that people have already mentioned but still no good. Had to take it to the garage in the end. And it turned out a lot of the wiring behind the control panel had burnt/perished, and needed replacing.

How much did that run to in the end to replace the wiring