Porsche Enthusiasts Club Forum

Yes that's the chip, the guys in the States claim to be able to repair it even upgrade it but the price is rather unattractive. Hardly cheap as chips.

I have already replaced that chip(IC4)LM2902N, actually the equivalent as now very hard to find the LM2902N; as I had the exact same issue as the Rennlist member mentioned. It wasn't expensive & took the CCU to a tech due to it having multiple legs, so was worth the try. It did not solve mine!

Mouser Electronics have 3900 in stock

My mistake!

Originally, Shibstead, the Thread Starter mentioned the IC4 LM2902DP was needed; IIRC this was difficult to find & the LM2902N is what he actually used & later edited. As you correctly mention is quite easy to find.

I feel really sick just blown a fortune on a new ccu and heater still does not work. It'll probably be a bad contact somewhere. So dig out the wiring diagram again and check all connections, earth points and continuity of wiring. My projector mod is working though, well o/s only on dip and it's a great improvement superb foreground with very sharp cut off, I forgot to order the correct harness.

I really feel for you mate as it's very tedious when these things happen.

At least you're making progress on the Projector Mod; did you buy them from somewhere, a link perhaps?

All working, went back to the beginning and checked the sensors again. Internal temp sensor reading a tenth of what it should be. I'd checked and rechecked them several times. Already replaced the mixer one. Did I read it wrong or was it trying to fool me or have I got the first stages of dementia. I feel such a twerp, spent a fortune when it was a simple cheap part.
The projectors are Morimoto H1 7s from emtuning.co.uk/ with reference to this post on Rennlist:-https://rennlist.com/forums/924-931-944-951-968-forum/802951-another-944-xenon-projector-mod.html I used Wipac old type Mini headlamps as a base and the bowls from same as spacers. I'll write it up with some photos.

Great! Please do a write up with some pics.

So, you just replaced internal temp sensor? May I ask how you checked the sensor reading as I would like to do this thoroughly? Also, where did you buy it on line as I think all three temp sensors are the same & if not expensive, might just replace what ever's hidden behind the dash!? I have the dash completely removed so will avoid going back there again.

Congratulations on getting it fixed, which is the main thing.

At least you now have a spare control unit which I'm sure you will be able to sell on in the near future. Lots of people are put off buying things from the States because of the duty hassles. You also now know your way around the 944 heating system so future fixes will be child's play.

Enjoy the heat in this cold weather.

Matt

I do believe they are all the same thermistor, ND03N00103J, RS part number 967-4465,

Yes they are all the same, the 2 internal ones are a simple thermister on mine, a bit tricky to get at but doable the exernal one was an enclosed type so a bit more difficult to do, if possible. It's the same as rear intake air temp sensor in a 993. I found the mixer one most awkward to get at, I dismantled the plug to feed it's wires through the grommet hole and did the soldering on the work bench but getting the grommet back in was a real pain, old hard rubber. should have used a new grommet. Did a run up to Fleetwood today (no, I was not feeling suicidal) the traffic was dire but at least I had a working heater.
There is a table in the workshop maunual which gives the resistance readings at various temperatures, mine were 17.85kohms @ about 10 c. not sure what the tolerance is. The faulty one varied a lot from same as rest to 0.2kohms which is why I missed it on first test and proceeded up a blind alley.
Found it.
From plug A:-
Outer sensor terminal 9 to ground;-
@ 0 C 34 kohm +/- 10%
@ 10C 20kohm
@ 25C 10kohm
Interior sensor (the one with the fan)
terminal 2 to ground
Mixer sensor (behind center vent)
terminal 1 to ground.
The thermisters are dirt cheap but complete sensors are either nla or expensive.
The heater on my old MGA was never a problem, levers and cables.

I have now tested everything, including temp thermisters again, still no success. HCV still won't shut off hot water supply! 2 theremisters read basically the same & the mixed chamber sensor reads around 1Kohm less, so not as accurate but still functioning.

​​​​​​​No idea what else to do!?