My new-to-me 1994 940 had no AC function - compressor would not run. I disconnected the lead at the connector behind the compressor and jumpered to the battery pos post. Compressor clutch engaged, no funny noises, and AC blew cool. After a major PITA and some help from this board, I got the control unit out and tested the circuit board. Dead relay, resoldering didn't help. Got a replacement via eBay from a wrecking yard for $40. Everything's cool, now. But not COLD, so maybe I need a recharge.

BTW, before obtaining the "new" control unit, I cobbled up a little 2-relay control module with a switch mounted in a spare spot on the dash, and spliced it into the AC wiring. All it really did was bypass the relay circuitry in the control unit - worked great, took about $5 worth of parts from my junk drawer. I can send the circuit diagram (Excel file) to anyone interested.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)

Check to see if you get 12 volts at low pressure switch to rule out the manual control unit. If you have 12 volts consisently, then your most likely low on refrigerant. These 940's are tough as Volvo's knowledge of AC appears limited, mine, thanks to Volvo has gotten much better. If leak isn't too bad, you can charge it every so often; otherwise, you need to start looking for the leak. Condenser is a good first place to start. If you end up opening it up, consider having a shop add a high pressure port so you can check the pressures. My 93 doesn't have a high pressure port, can't imagine they added one for 94. Good luck.

If the compressor is not turning on AT ALL, I'd go for the control panel. I had the same problem. I removed the control panel and re-soldered the connections on the circuit board. Take note of the A/c compressor relay (small black box on center of board). My A/C compressor now works and turns on normally. It's ice cold too! It is time consuming to remove the A/C control panel...you have to unbolt a metal bracket that holds the bottom two screws on the face, then carefully disconnect the wiring and vacuum lines from the back of the panel. Good luck! Once you get to the circuit board on the control panel, you should see a poor factory soldering job. The circuit board is under a metal bracket btw.

If you jumper the pressure switch, and it starts running, then the charge is NOT ok. 90% of a/c problems are because of a refrigerant leak.
I've chased multiple problems with these same cars before- hoses, compressors, seals. Seems to be a tough car to keep working right.
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Rob Bareiss, New London CT ::: '86 244DL- 215K, 87 244DL- 230K, 88 744GLE- 198K, 91 244 180K