986 electrical issue - please help

[MWS-Indy]

Question regarding '01 986... I have had car in storage for about 3 years and have been working to bring back to life. Have had many electrical gremlins, have resolved all except:

Climate control unit- fan stuck on high, display dead, only way to shut off fan is by pulling 30A fuse at position D6. Checked all fuses, ok except 7.5A at position E7 (air conditioning system). Replaced fuse (here is where it gets weird) and without key, when fuse is inserted dash lights up, all systems active (as if key is in acc position). Checked voltage w/ at fuse, shows 12v when key off, 0v when key on. Just out of curiosity, I inserted fuse while car was running and when key was removed, engine kept running!

As FYI, with 30A @ D6 and 7.5A @ E7 removed, all electrical systems ok. Suggestion PLEASE. :)

[Ahsai]

D6 is always hot and E7 is switched power. It sounds like your climate control module is bad and it leaks power (from D6) back to the switched power source even when the key is removed. I suggest you remove the climate control unit and send that out for dagnostic. If my theory is correct, once you removed the control unit, everything else (non a/c stuff) should work as normal.

Is your fan also controlled by the control unit or there's a physical dial knob to control speed?

[MWS-Indy]

Fan electronically controlled by climate unit, no dial, just buttons to adjust speed. Also, if E7 is switched, wouldn't it read voltage only when key is on? It's just the opposite, when voltage tested @ E7 terminal, voltage reads 12v w/ no key, 0v with key in acc position. What really has me stumped is why E7 w/ fuse would keep car running without key. Btw, we are on same page, my next step is to remove climate unit to see if breaking the circuit solves this issue (and means new climate control unit). Thanks, and additional input really appreciated! :)

[MWS-Indy]

Also, I am thinking it must have something to do with switched power as the 10A fuse on back of CDR head unit was blown, replaced that and at least now I have music...too bad I don't have heat. :(

[Ahsai]

I agree the E7 measurements were weird. E7 and B5 to B10 are on the same circuit (wire) and they get power from the ignition switch. If E7 is 0v (assume the fuse is there and it's good), fusses B5 to B7 will also be 0v too, which is hard to believe.

[MWS-Indy]

Ok...update. Pulled the climate control interface and checked the voltage on E7, looks back to normal. Next was to disassemble the climate interface and found one of the I/C chips was bubbled (arg!). Now I am trying to figure out if the board caused the problem at the fuse box, or some issue (not yet found) caused the board to burn out. Hate to buy a new climate unit just to fry it too. Might be the old adage of the 1000 dollar part blowing to protect the 50 cent fuse.

What would be wonderful would be a donor part to see if that fixes the problem, but I fear that isn't going to happen....

[Ahsai]

Perhaps you can try to power up the control unit on the bench separately by another power source. That should help you troubleshoot it without damaging the car.

[MWS-Indy]

Thanks again for your response, but I know the unit is bad (visual inspection & multimeter), my question would a replacement unit be damaged by some unknown electrical issue with car? I doubt it, but hate to by a new unit just to burn it out immediately. At this point I am thinking that I might leave this one to my local Porsche dealer. It might cost more (ok, a LOT more), but the part would be new and I wouldn't be running the risk of potential damage to a replacement part. Will call dealer tomorrow to check price, and if it's under $1500, I will go that route and leave happy... Poorer, but happy. Guess money can buy happiness, or at least parts. :)

[Ahsai]

Makes sense. I came across this shop http://www.systemsc.com/ and this thread http://rennlist.com/forums/964-forum/559015-964-climate-control-unit-failure.html

 

Looks like they may be able to help in your case. I agree though you may want the dealer to take all the risks on this one.

[MWS-Indy]

Final thoughts: I have considered a "reconditioned" unit, but am concerned with quality. As the unit I have now was replaced in '09 (and has no wear and probably less than 1500 miles of use), I considered trying to track down the Hella control board and rebuild myself, but think with possible other electronic issues I will go the dealer route. Replacement (with labor) should be less than $1000, and any electrical issues should be diagnosed.

Big thanks to Ahsai for thoughts and input... Much appreciated!

Lesson to share: It is POSSIBLE for a faulty climate unit to complete (somehow) the ignition circuit. Two dealers and an independent have never heard of this, but I can tell you it happened. Wish I could submit a picture of my running car with key not in ignition, but somehow I think the context would be lost. :)

Porsche... Is it more fun to drive, or to try and figure out why you can't? Guess it depends on the weather.... ;)