When the AC works, it works great. It intermitantly decides not to, and it's usually at a time when I can't check it (on my way to work.) But today I had the fortune of a morning off and the AC decided to quit on me in the driveway. It's electrical. How's the AC button tell the compressor relay to turn on?

Some back ground:
I've read through the FAQ A/C post in tech/misc, and I already had a good grasp on the operation of the AC system. I've got good high and low side pressure. Compressor clutch doesn't kick on when I tap it with a hammer, so it's not shim spacing. I dont have leaks. I've worked in car audio for a few years now and have a good understanding of 12v electrical.

So with the engine running and AC on, but no compressor spinning, when I remove the compressor relay and multimeter the relay coil slots (85/86) they have +/-0.1 volts. This tells me SOMETHING in the BCM/climate control array isn't switching the power to the compressor relay. I confirmed this by shorting out the supply/load pins to each other, at which time the compressor engages, fan turns on, and cabin temp drops without fail. So what is between the AC button and the relay that could randomly mess up? Does this particular car have an AC system thermostat that is somehow malfunctioning? The light turns on in the AC button and everything, but the relay doesn't get the message. Factory wire colors and routing location/functions would be helpful. Would I damage anything by bypassing the OEM wiring setup?

 

 

So I might have a faulty evaporator temp sensor...