996 tt MY 03 Aircon acting funny

Hi Everyone, has been a while since my last post, guess it was in the aircooled section� Since my 993 is gone, I have changed to a 996tt MY 03. Car came from California back to Germany. I have it since 2,5 years. Now I have a really �funny� error, where nobody in Germany could help. I have trouble with my Aircon. Last year I changed Condensators and the dryer(?) the one looking like a soda can. filled up the system. => system worked just fine. end of last years season, I had a short on the engine bay 12v socket. Long story short, the cover was open, a tool fell and somehow shortened it for second. I don�t know if that�s causing it, but I just mention it. No other issues, no blown fuses, no errors. Adter that, and I don�t know how long apart, but couple of days to weeks. I recognized my AC to no fail. AC is currently not working at all, no cold air. System is filled and not leaking. When I start the car, the AC Control unit is working. All functions can be pushed, flaps and vents are working fine. Adjusting Fan speed and temperature are working and resulting in expected behavior. Now the fun begins: if I switch of the car and restart, or just go to position 1 with the key, the control unit is off. It�s completely dark, and dead. when I wait for another period of time (pulled key) or the car was locked and closed for approx one hour, displays are back on. But no AC. I can reproduce that issue. what didn�t do so far: changed the ignition switch. The one behind the ignition key. It was already updated to the new version with part no 4B� I checked all fuses. No faults. I checked all relays in the front next to the fuses and under the back carpet next to the DME. No faults i changed the control unit, as I thought this is broken, but no change. The new unit has the same problem. So, big question: what causes the symptoms? what causes the control unit to turn dark after it was on and permanently disable AC? every idea, even the most stupid one is highly appreciated! thank you all! Sorry for any typo, but English is not my first language. best regards christian edith: posted in 996 as the AC is the same and not tt individual.

If anyone would have a good wiring plan, it would be highly appreciated! thanks christian

Well, sounds like you started troubleshooting with a logical process of elimination, good start. Next I'd start the engine, get the control unit on, the fan in high speed on cooling (you did say control unit does work intermittently and u can get it on..?) Verify the compressor is not running. Then unplug the compressor control plug and power up its clutch with 12v just to check the refrigeration circuit and make sure its still intact and blowing cold. If compressor does start and blow cold, next I'd check the compressor clutch relay. And check pressure switches for continuity. Let us know what you find.... Not sure what u mean by "no faults" when you checked all relays..? Or what "I had a short on the engine bay 12v socket" actually means..? to check the ac compressor relay I'd disconnect it completely, then apply 12v to control side of relay while checking power side with meter for continuity/no continuity.Then you know for sure the relay is operating or not. jmo Sure sounds like a ac control panel is intermittently not working. you say you've replaced it with a oem brand new one..?

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it should mean now faults. Now it�s faulty.. Secondly, I have grounded the 12V socket in the engine bay, which means in german to short a circuit. hope to have clarified. the relay is the one under the Bose subwoofer or rear carpet, right? Yep. Same behavior. either on and seemingly to work or dead with no function.

Under the carpet behind seat

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Sorry, still not clear on what you mean. in troubleshooting it helps avoid chasing our tails too understand one another precise and clear. "it should mean now faults. Now it’s faulty.." So does the relay test good or bad..? I assume you mean the battery jump point housed in a closed plastic insulator box? " I have grounded the 12V socket in the engine bay"

Sorry, my bad. English is not my first language. you are right, the battery jump point. All fuses in the footwell compartment are OK. No fuse was broken. I pulled all relays, in order to check impact on the the control unit. I will check the relay and apply external 12v to the Compressor to see what happens. but still no clue why both control units are acting like that.

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Yes, understand English is not your language. You do pretty good with it though. Don't misunderstand me please, not trying to be condescending at all. Just trying to make sure we are talking about the same things to make the correct troubleshooting suggestions. yes, once we determine the refrigeration circuit is intact we can move to the control circuit and try to troubleshoot that. I'll look for a schematic/pin out of the ac control unit. Intermittent problems are the hardest to troubleshoot.

Thank you. no hard feelings at all. just lost in translation. today is not the best evening to try, as we only have a little above freezing point. it�s a*s cold�

Update: my hands looking like I had a fight with a cat.. the connector for the clutch is below the SAI Fan� relay ok. Clutch OK, cold air coming. in that sense, it has something To do with control unit, or the electrical supply of it. I doubt two control units failing with same error, one factory new.

Question: is one of the main fuses behind the glovement compartment (12V distribution point) only related to the ac control unit?

Update: the 12V Distribution Box is fine. Alle fuses ok. What a mess to get there� I was working all day on the error and the following occurred: the control unit seems sometimes not to �start� As mentioned usually the display turns on during the initial start, but does not turn on, once I switched off and on again. I checked switched plus(?) on the unit. The black and blue as far as I know� even if the unit does not turn on, switched plus is available. so, I took off the black plug and left the red attached (unintentionally) and the fan started to work on medium speed immediately. after re-connecting the black plug, the display turned on. Sometimes i had to do this 2-3 times, in order switch on the display. Any ideas??? anyone a Pinout of the CAN version available?

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Are all plug pins straight/clean/making good connection...? Sure sounds like an intermittent bad connection..? Been looking for a pin out, haven't found one yet. Seems you're on the right track confirming the ac panel has + 12 volts when ignition is on. Not sure if another trigger voltage is needed from dme..? or other sources. Sure seems like a faulty ac controller panel, but this is a brand new oem controller panel..? I've changed out 1 that would not light up or turn on. Got ECU Doctors to fix it. Changed out another one that lights up and fan went on but no compressor, with a Ebay good used one. After changing them out all worked fine. A pinout would help. Maybe PT3 (he knows all) will see this and chime in....

Yep, factory new, who is PT3? can we link him into this topic?

No one a pin out of the control unit? no one ever had something similar and has a hint to provide?

I would imagine a Bentley manual would have the pin out. I look if i can get to mine burried in the garage. wiring diagrams r all over the place on the web for this car.....none coming up on a google search?

You need the Climatronic wiring diagram for any 996 or 986 Boxster, the air conditioning wiring is the same for all of these. Power comes from Fuse D6 for the blower fan, Fuse B1 for the constant power, and Fuse E7 for everything else. The power from Fuse E7 is pin D9 of the large black plug. This is switched by the ignition switch. The power for the blower fan is pin B11 of the red plug. This is switched by the load reduction relay. Constant power from Fuse B1 is pin D7 of the large black plug. Ground is on pin D15 of the large black plug.

I know almost nothing about the HVAC system, but I wonder about that ignition switch. Are the fans also not blowing when the AC isn�t working? If yes, see this: https://www.renntech.org/topic/15000...n-not-working/

Hi, currently a few days away from home. the ignition switch is factory new and upgraded to the new version. what I really wonder, mean and high pressure valve getting signals. where else does the system get a signal from? From the DME?could the dme be faulty? I have no ther issues. Could I permanently with a switch bypass the system and trigger 12v to the magnetic clutch?

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Yes you could power up the clutch with a switch, but you say the a/c controller panel doesn't go on all the time?, so how will you control all the vents/temperature and inside fan speed...? Any rodents in Germany..? Thinking you've got some wires partially chewed up by rodents that intermittently make and break contact..? Rodents love the soy based wire insulation. They chewed thru my o2 sensor wires in the engine bay. I'd follow the info theprf gave you. I'd check each of those circuits for voltage. Then trace and repair as needed. You should be able to at least get the brand new oem control panel to go on each and every time the ign is on.

I measured again at the Relais. I am getting +12V from clamp 30 and 86, which is good. i am having +3,6v from clamp 85 to 31. to my understanding, this should be 0, as both ground. where does the white and green cable go? thanks!

This is where the regular 996 wiring does not match the turbo wiring. The white/green wire goes to the engine ECU, connector D (which has 40 pins), pin 27. It turns on the A/C compressor relay.

Uhm� that�s means faulty DME???

I would suspect a faulty wire first. Check the voltage at the DME. I use a sewing pin pushed into the wire insulation to connect my voltmeter.