My problems were similar and were fixed when I replaced my coolant thermostat. The ac compressor has a temp relay which will activate when the compressor overheats. I noticed the compressor quit working when the car warmed to temperature so i tried a new thermostat and have had no probs since...Worth a try for $5.00...

Check your connector to your low side pressostat. All the tech did when he jumped the wire at that switch was tell the compressor it had enough freon to come on. Then he plugged it back on. Obviously, his "jump" wouldn't have worked any longer than the precise moment he did it, therefore, we can assume that what really fixed it for those couple of days was either the wiggling of the connector on the low side pressostat, or the wiggling of the low side pressostat itself. Your dramatic acceleration could have wiggled either of those things. At the very least, I would say you need a new connector, and/or a new low side pressostat.

Chris

Who ever designed the wireing system for Volvos is probably the same guy that wired my home. I would like to attach him to my generator and then get the car up to 130mph.
"No flashing lights" What a great clue! Fix that and your A/C will probably work again. Your "dramatic acceleration" created enough "G" force to let a loose connection connect. Take off the glove box.

Klaus
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95 854T, 88 780, 88 245

I don't know if this will help you or not but I had the same problem with my 92-940 just last summer. I just bought my wife an 850 so I don't know if the system is set up the same way. Here goes.

My 940 had the exact same symptoms that you describe your 850 having. I did all you did and bypassed everything using a paper clip at the evaporator. I finally got tired and called the dealer and talked to the tech supervisor and explained my dilema. Behind the glove box (that I had removed) there was a hot lead that went to the dash switch which turns everything on. I found (with a test light) that sometimes I would not get power to the switch assembly. The tech supervisor told me that the black lead that feeds that switch is behind the glove box and that it is a white clip (the kind that snap together) connector. He told me to look inside the connector because the connection is usually cooked on the inside of the connector and you can't see it unless you try and separate them by pulling them apart like you're trying to disconnect them. Sure enough, it was cooked and all I did was hard wire it with a wire nut, no more problem!!

Hope this helps you.

Henry

97-850/76k,92-940/224k, 91-740/178k.

From everything you just described, I would suspect the compressor relay.Replace it. You have done everything else.
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'82 240DL Stock / Masters Class, '94 850 Fully Loaded / Daily Driver, CVC / VCOA Member http://www.capcan.com/tonyg.htm