Questions on heating

[PSH]

Hi guys

Does anyone have the part numbers for the usual suspects when there's 'zero' heat, I have lived with this for a long time but now want to sort it out once and for all. I have tried to read what info is available on the internet, alas Clarks Garage doesn't seem to be working. I know that there are plastic clips and solenoids which can fail and give you no heat which I'm hoping is the case here, I just need to know what/where these parts are before I start taking things apart, I'd like to start with the easy possibles first.
Some background info, '86' 951, the car is running fine, engine temp is fine, vacuum valve on the bulkhead works, heating pipes going into and out of the interior are both hot, the heating matrix was cleaned with pressurised water and showed no signs of a blockage, clean water went in and came out, no muck. Fans work, defroster works (no heat), A/C is fully working.


If anyone here has had a 'no heat' issue and fixed it, could you please give me the part numbers of what was required, I'm happy to just buy them, ready for when I take things apart, I believe that most cost very little, I just don't know what's what under the dash as I've never taken it apart...not yet at least...

Cheers

Pete

 

[Waylander]

Hi Pete

I have just been on clarkes and its working fine

I can help out with a 968 heater controller for testing but it not an AC one,
if the hot water is going in and out of the matrix you should feel some warmth in the cabin even if the fans are not running, the solenoids and valves can be manhandled for testing,

I can also help out with some thermistors if you need them, I have a few

 

[marojojoem]

Pete, my 86 951 had similar symptoms, no heat except when the defrost button was pressed if I remember correctly. Turns out the ambient sensor which lives under the plastic cover next to the fan assembly was goosed so the system thought it was permanently tropical, hence no heat! Easy fix if that's your problem. Mark

 

[scam75]

That's a good point. Does defrost provide heat or not? I'd be assuming no based on your posts so far right enough.....

Stuart

 

[PSH]

Thanks for the replies so far guys, please keep them coming...regarding defrost...No I get no heat when using it, not sure if I should or not?.
I forgot to mention, that sometimes I do get a little heat but it only lasts a few seconds and not very warm...This occurrence is very rare, perhaps once or twice over a year.
regarding Clarks Garage, yes the page opens and you can access the various sub-pages but I can't open any of the links in the 'GarageShop Manual'? they highlight but won't open for me?

Please keep the answers coming as I'll print them all off and use to help when working on the car...part numbers for the various parts would be most helpful...

Cheers

Pete

 

[Waylander]

I find that if im using google chrome as a browser, you have to right click on the link you want and use open in a new tab or page, that works

easy to test the thermister under the bonnet,

heres the link for clarkes http://www.clarks-garage...shop-manual/hvac-01.htm

thermistor values: 928 but should be close
https://rennlist.com/foru...-thermistor-value.html

 

[Waylander]

under bonnet / outer sensor 964 659 120 00 @ 43.14
Air Box Sensor PCG 653 121 00 Repair Kit @ 99.13
Servor Motor / dfrost flap/footwell 944 624 119 00 @ 239.96
Servo Motor / mixing chamber 944 624 120 00 NLA
Interior Sensor 944 624 013 00 NLA

 

[Waylander]

I also found that my interior sensor was a bit flakey, took the glove box out, removed the hose from the interior sensor, looked in the end of the fan motor unit and it was completely choked with fluff and crap, it needs cleaning out but in the centre of the airflow is the glass thermistor, its tiny and easily damaged, I used a combination of tooth pick / kabab stick and a can of compressed air to clean it out

 

[PSH]

thanks, Martin... do you by chance know the part numbers for the various plastic clips which seem to be a common failure?

I know nothing about these thermistors....what do they do (I guess sense temps) , where are they, how many would I need to replace all?

Pete

 

[944Turbo]

If it is a servo motor - I successfully dismantled and cleaned one of mine that had locked up back when I had my red car, I think there is a process in the manuals for checking the operation (applying 12 volts to the various terminals IIRC)
Tony

 

[944Turbo]

thanks, Martin... do you by chance know the part numbers for the various plastic clips which seem to be a common failure?

I know nothing about these thermistors....what do they do (I guess sense temps) , where are they, how many would I need to replace all?

Pete

I think there are three one by the intake to the fan housing in the scuttle (the most common failure) one at the end of the pipe that runs from the circular vent in front of the passenger (air sucked through pipe by a fan in the passenger footwell - often gets full of fluff etc) and I believe the third is behind the centre air vents but that is the one I am least familiar with!
Tony

 

[944Turbo]

Oh and a thermistor changes resistance with temperature to provide feedback to the heating controller, If they are sending the message 'its hot' you wont get heat out of the heater!

 

[PSH]

Thanks, Tony, do you (or anyone else) by chance have a link to the manual page that gives the info for testing the system? that would be most helpful..

Cheers

Pete

 

[Waylander]

starter for 10
http://www.clarks-garage.com/shop-manual/hvac-01.htm

Its in the Chassis vol3 Section 80 >> onwards https://porsche968.s3.eu-.../944/Vol3x-chassis.pdf

 

[PSH]

Thank's Martin, I've already printed that off thank's to your earlier info re Chrome, I've not had time to read it yet..You mentioned that you may have the thermisters...can I ask the price please, PM me if better. I'll try to get my son to do the various tests to pinpoint what's actually failed first. Trouble is, my son is in such demand he has little time to spare for his old man these days...I fully understand though...poor chap rarely gets a day off or home before 9 pm each evening, works all weekend too..

Pete

 

[Waylander]

PM Sent,

the one in the mix chamber is the proper pain in the ass,
the one under the bonnet is easy as
the one in the interior temp sense fan is also easy, just fiddly

or if you wish to order some
they are part number RS 697-4465 or ND03N00103J

 

[PSH]

I thought these were clear glass sensors...did I get this wrong? alas, I don't have an RS account..

Pete

 

[Waylander]

you don't need an account you can order by card from the website, the 30 year old ones were glass...........................

 

[PSH]

ahh.. thanks Martin...that makes things much clearer...

cheers

Pete

 

[PSH]

ok, I've ordered those...thanks for the heads up..when in a past life I was a company buyer, mere mortals couldn't order from RS without a company account, how things have changed...

Pete