Based on a lot of advice I have received on the board, most recently from Jake, I swapped out the a/c relay behind the glove box in order to try to stop the tick-tock sound coming from that relay (which is signifying the compressor turning on and off). Those who have heard my saga know that, last time I had it checked, I am not experiencing that sound due to being low on refrigerant (the usual reason). So it's got to be something else, and my next stop is the a/c low pressure switch (a.k.a. the pressostat)

Jake, if you're out there (or anyone else who can answer), you told me that I can replace the pressostat without losing refrigerant. I just want to reconfirm this. Why won't I lose refrigerant when I tap into that line?

And just in case anyone is interested, I have signed up to receive access to all the Volvo 850 TSBs through Alldata.com. It cost me $24.95 a year and while there's not a wealth of information, there's a fair amount. At least now I have access to all the TSB detail and not just the titles. If anyone wants to get more info about that you can go to www.alldatadiy.com

Rich answered the switch Q BUT although I know you've said that you're sure that your freon level is full, I still question that as your problem really sounds like a low freon problem more than anything else.

I don't want you to waste money and time by guessing at all the various switches/devices that may not ever change anything for you.

Can you get a second opinion on the freon charge? You'll need to go to a shop with a recovery machine because the ONLY way one can know what's in there now is to recover the freon as the machine then weighs the actual amount removed. If it weighs less than 1.65lbs, it's low and has leaked out somewhere. Now, if it were my car and I was just losing a slight amount every year, I'd just add the missing freon and in most states you can still do that with 134a. If it's wintery (cold) in your area now, I'd wait until spring when you'll need it again unless you're defroster isn't working as it doesn't work well w/o the AC compressor running.

There is a schrader(like a tire air valve) valve under the low pressure switch, so when you unscrew it you won't loose all of your R134a.