944 heater always on troubleshooting

[Latitude48]

Thanks for the video link... really nice to see how this works. My records show I purchased two each of 944 572 314 00 Bearing, Connecting Rod, and 944 572 217 00, Spring Clip, Connecting Rod. The PET says three each are used. I'll have a look to see what I can find out, but I'm still planning to replace the HVAC controller... I have it, might as well use it, ha, ha.

[Tom]

Here's our diagnostic guide for the cc unit too, if helpful...

viewtopic.php?t=357

[Latitude48]

Test results: with the engine running, turning the temperature control from cold to hot or vice versa does nothing; the heater valve is always in the fully open position. I pulled off the vacuum line and manually closed the valve and placed my finger over the port and let go, and the valve defaulted to the open position, so it seems the valve is faulty, which isn't surprising as it's never been replaced.

Since the S2 is due for lube service I'll just have the shop replace the valve as it's much easier to get to with the oil filter removed (the S2's valve is just off the water pump, behind the filter).

I'm still going to change the HVAC controller as I'm tired of the broken end always detached and "popped up" from the dash.

As an aside: I have a red 968 emergency flasher switch I'd like to install. Other than the two screws at the HVAC controller, and what I assume are two more under the little cover at the outer door end, does anything else need to be detached to pop off the trim... like the air temp sensor screen? Please advise if anyone knows. Thanks.

[Tom]

Test results: with the engine running, turning the temperature control from cold to hot or vice versa does nothing; the heater valve is always in the fully open position. I pulled off the vacuum line and manually closed the valve and placed my finger over the port and let go, and the valve defaulted to the open position, so it seems the valve is faulty, which isn't surprising as it's never been replaced.

Since the S2 is due for lube service I'll just have the shop replace the valve as it's much easier to get to with the oil filter removed (the S2's valve is just off the water pump, behind the filter).

I'm still going to change the HVAC controller as I'm tired of the broken end always detached and "popped up" from the dash.

As an aside: I have a red 968 emergency flasher switch I'd like to install. Other than the two screws at the HVAC controller, and what I assume are two more under the little cover at the outer door end, does anything else need to be detached to pop off the trim... like the air temp sensor screen? Please advise if anyone knows. Thanks.

You might have the shop confirm your test with a mityvac, but sounds like you found the issue.

Here's an excerpt from the Carpokes dash removal pfd showing all the screws holding that trim on.

trim-removal.jpg (486.6 KiB) Viewed 438 times

[Latitude48]

Thanks much Tom! You are a repository of immense knowledge. Can I assume that little sensor cover unscrews counterclockwise... you never know with "German Engineering."

PS - regarding my heater valve test, before disconnecting the vacuum hose I tried pushing the lever closed and I could hear some air leaking out from what I thought was the rear of the diaphragm area, so I do think it's INOP now.

[Tom]

The little rosette doesn't really thread in. It just has a couple of tabs that lock in place with a quarter turn. I can't remember if it is even directional -- it might come out either way. Just turn it with your fingers one way and/or the other, and you should have no problem.

[s14kev]

It looks like my pin A4 supplies 12V and then switches off shortly after. I guess the next step is to source a CCU to swap in.

@ROB III Yes, that was me with the white with blue script RS backdate.

[Tom]

The cc unit is probably bad, but before springing for a new one, be sure to test the temp sensors. If one of them is bad, I could imagine the cc unit being tricked into thinking the cabin needed heat. I'd also play with the temp knob a bit -- does it do the same thing if you turn it up just a little above the blue dot? The knob is just a potentiometer and they tend to develop bad spots in their range when they get old (like the AFM and old scratchy radio dials). If it's just the pot, that would be a doable DIY repair...

If none of that helps, and you end up getting a replacement, I'd be interested in buying the bad one as a core.

[Latitude48]

Looks like new... because it is new And well, well, well, no more hot air when the temp is turned down! Guess that heater control valve wasn't faulty after all, but I'm still going to change it. The heater control valve is no longer available from Porsche, although Pelican has a few for the bargain price of $130+; the URO is about $19. Now all I need are a couple of new $31 slider knobs from Porsche and I'll be ready to start tearing apart the other side of the dash to fix the broken odometer.

PS - I used a Nickel to remove the little vent cover. It looks like it can be removed by turning CCW or CW.

Edit: I tried to order another red 993/968 emergency flasher switch for the 951 from Sunset Porsche and the current p/n 944-613-235-02-N05 isn't currently available because Porsche is changing suppliers and waiting for test parts to confirm quality.

[Tom]

Nice work! I just checked a spare heater valve and when I force the valve closed and put my finger over the vacuum port, it stays closed forever. So you are probably wise to change yours anyway if it opened when doing that. The constant vacuum from the engine might be enough to keep it closed for now, but I imagine a small leak now will become a big leak later.

Are you missing the slider knobs altogether or are they just loose and fall off? If just loose, our hand-dandy insert will fix that nicely and I'd be happy to send you a set gratis.

https://www.carpokes.com/viewtopic.php?t=877