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I always thought that normal operation is the inverse : The A/C is meant to be disengaged when you floor it.
 

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Discussion Starter #22
So just spent 4 + hours at the garage. We removed the control unit, swapped over the sensor ventilation fan, and then when we cracked open the box the connector for the ventilatilation fan was broken off the circuit board. Fixed that, tested, and it didn't work. Swapped the temp sensor over, still didn't work, however the diagnostics was no longer giving an error code. They then hard wired the compressor to the battery and it worked perfectly, so the problem is clearly control-related. However I am out of time (off to senegal tomorrow) and out of parts. I guess the next step is to buy a complete new control unit.
 

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Discussion Starter #23
To wrap this thread up and just in case anyone has a similar fault in the future.......I have finally found the solution to my AC problem. The car was giving a fault code relating to the brake switch. I had put this on my to do list but hadn't regarded it as urgent, and certainly not expected it to interfere with the AC system. But, replacing the £10/12 euro switch has completely and instantly fixed the AC problem. A little frustrating when I think of all the effort that me and others have put into this, and quite a bit of cash thrown at it, but very relieved to have finally fixed it, even if I don't understand why! Thanks for all the help.
 

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The failed brake light switch must have had an effect on the wide open throttle signal. Correct operation is to cut compressor at WOT not allow it to run.
It must work in such a way that seeing brake being operated some how stops feed to the WOT signal or something???
Very odd fault and I don’t think you are alone in thinking a brake light switch wouldn’t cause air con issues. Got to love Italian wiring.
 

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Discussion Starter #25
The failed brake light switch must have had an effect on the wide open throttle signal. Correct operation is to cut compressor at WOT not allow it to run.
It must work in such a way that seeing brake being operated some how stops feed to the WOT signal or something???
Very odd fault and I don’t think you are alone in thinking a brake light switch wouldn’t cause air con issues. Got to love Italian wiring.
hmmmm interesting speculation Johnny. I had understood that the sole function of the switch was to turn on the brake lights, however your suspicions do suggest that there is some connection between the two systems that could have well resulted in this fault. How about this then: during the various prior attempts at fixing the problem I had the stereo and AC control panel out, and when back in, the steering wheel stereo buttons no longer worked. Likewise the ABS warning light came on after removing the gear selector panel and refitting it. Both faults have also magically vanished upon replacement of the brake switch! As you say.....gotta love Italian wiring....
 

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Brake light switch is there for more functions than just the lights. It's part of the starter circuit for one thing. Car won't start without brake or clutch (or both) pushed down just for one example.
 

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Discussion Starter #27
Yeah good point - though in this case the car still started...but point taken. Still seems very odd to me though, especially the interaction with the steering wheel borne stereo controls!
 

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To wrap this thread up and just in case anyone has a similar fault in the future.......I have finally found the solution to my AC problem. The car was giving a fault code relating to the brake switch. I had put this on my to do list but hadn't regarded it as urgent, and certainly not expected it to interfere with the AC system. But, replacing the £10/12 euro switch has completely and instantly fixed the AC problem. A little frustrating when I think of all the effort that me and others have put into this, and quite a bit of cash thrown at it, but very relieved to have finally fixed it, even if I don't understand why! Thanks for all the help.
Thanks for this post, my aircon failed and the only fault was the brake light switch, and the specialist couldn't find any faults. I ignored the brake light fault, but did buy a replacement, as the brake lights were working but after reading this thread I changed it and BINGO, a/c now working. Thanks a load!
 

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Hello guys
I Have the same problem with the temperature sensor fault.
Can i know where is the location of the brake light switch you changed so i can give it a try maybe i save some time and much money please?
 
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