heating advice sort

[PSH]

Hi guys

I would like to pick your brains in relation to a heating issue that I thought was down to a blocked matrix but not so sure now...The heating hasn't worked properly for some time and since the rebuild 2 years ago I've had no real heat at all. I thought this may have been due to the matrix which was leaking coolant (had been for some time) and after we used a sealant mix to seal the leak we had no more issues with coolant loss but did have zero heat. We tried back flushing the system with little effect although, for about ten minutes after we did have a little heat but it was very little, nothing dirty came out of the matrix during backflushing. The pipes leading to the matrix were both hot which again suggested to me that the matrix was blocked and the water was just bypassing the element itself.
The fan switch works properly at all speeds and the thermostat was tested when the engine was rebuilt, I do have a new one awaiting fitting at some point just in case.
Now wind forward to yesterday and after the Rutland meet I was driving to my daughters for dinner when after about 10 miles the heating began working and worked well, this continued for the next 40+ miles to my daughters.
We had dinner and left a couple of hours later, this time we were back to no heat and having to use the demister intermittently to clear the windscreen due to the cooler night air, however after 15 minutes when I turned the demister back on to clear the screen again the heat came back on full blast for a few minutes and then stopped again?
I guess it's possible that the matrix is clearing for a short time but not really convinced of this, however, i did lose a little coolant which suggests the seal failed and perhaps it was during this that hot air was released?
Now I've worked on just about every part of this car but the heating is one of those areas where it's needed little, attention from myself and hence I'm asking here if anyone has had similar symptoms and if so what was the cure? As most of you know it's an 86 with full climate control, I read that later models had A/C and not climate control to save cost, I don't know if this is the case but mention it in case I have more sensors etc that I need to look into and where someone may have had this problem on an 86 turbo in case there's a difference?
I was going to just buy a new matrix and fit it when I redo the dash but don't want to waste money on something that I may not need...

hoping someone has been there, got the T-shirt etc...

Pete

 

[bmnelsc]

This is from a post on the Porsche Club of America site and describes how the climate control works on the S2s which I think is the same for all later 944s. I suspected from your description that you are having air flow problems rather than water flow problems...this post describes the workings pretty well but doesn't go into troubleshooting the in dash temp sensor, etc that participates in the system.

Q: 1990 944 S2 Cabriolet heater does not work but defroster blows hot. what could this be caused by?

A: Heater/defroster challenge
Submitted by Bill Burris [GPX] on Wed, 01/21/2015 - 11:19
This condition is likely caused by a heater flap control that is stuck in the defrost position. The linkage fix is relatively simple (see sites like www.kronowit.com/porsches/944-heater-fix.html (link is external)) but for many owners the prospect of lying on your back with your feet through the window doesn't sound like much fun so you may wish to take it to a qualified Porsche repair facility for diagnosis and repair. There's also an outside chance that the heat/AC control panel has given up, but those failures are more rare, so start with the most frequently encountered problem first.
You may be interested to know that the heater core is engineered to run full hot whenever the control unit indicates that heat is required. The way to get less than max heat is to blend in ambient air either from outside or from the passenger cabin (recirculation) using what NipponDenso calls a 'blend door' to manage the temperature. The environment control built into your car is a relatively sophisticated system with temperature sensors, blend door and footwell/defrost distribution motors in addition to the slide controls and temperature setting knob on the dash. Some of it is manual (the A/C compressor switch, for example) and others automatic (like an override for full defrost.) Thankfully, the system has proven to be quite robust over time, so hopefully the fix in your case is simple and you'll be back in control - no longer at the mercy of the heater ninjas.




Bill Burris



Clark's Garage has an excellent section on this with good graphics but talks mostly about heater failing to full hot - great overview of the system tho.
www.clarks-garage.com/shop-manual/hvac-01.htm

 

[PSH]

Thanks for the links Bill, I will check what they both say, although my issues aren't exactly the same the pictures/drawings will hopefully give me a better understanding of what's what...

cheers

Pete