When my A/C died on a '95 940, it was loss of freon. Push the A/C button and nothing worked. After chasing all over the wiring etc.. as suggested here, I took it ot an A/C shop and there was no freon. Nothing works if the low pressure switch isn't made! Replaced the leaky condensor and it's been BRRRRRRRRRRR ever since.

I haven't read the FAQ, but to check and see if the AC control unit is sending the signal, I get a test light, and see if I have power to the low pressure switch. Open the hood, see the silver cannister in the rear of the passenger side engine compartment? See at about 2 o'clock the connector on a switch, that's the low pressure switch. Press down the little clippy doo (technical term)to release the connector from the switch, and see if you have power to the connector. No power = need to repair control head. Yes power = problem elsewhere. Next, jump that switch, see if the compressor comes on. If the compressor comes on, you either need a low pressure switch, or you are out of freon. If the compressor does not come on, you either have a bad power wire or ground wire to the compressor, or a bad compressor clutch. Hope this helps.

Chris