---96' Volvo 850 GLT with ECC AC.

A mechanic told my wife last summer that the compressor probably needed shimming. After researching and deciding he was probably right, I decided to at least check the freon before I tackled removing the compressor.

I read that it should be around 25 lbs on the low side so this morning after driving 40 miles not using the AC and the ambient temp around 65d, I raised the hood to check it. With the AC turned on I hooked up the pressure gauge and found that the clutch would engage and the pressure would climb to around 45 lbs. then dis-engage until it dropped to 25 lbs and then re-engage and repeat over and over until it finally wouldn't engage anymore (about 3-5 minutes). Then the pressure climbed to 85 lbs. without the clutch engaged.

Doesn't this seem more like a pressure and/or pressure switch problem?

Same situation mine had before it quit working (why it quit was another issue though I believe).

Mine was due to improper refrigerant pressue (too low on mine). Once it was brought back to proper pressure it worked. However the 850's must be recharged under a vaccuum for them to work properly. Simply trying to use a recharge can from an auto store doesnt work and will probably just get you over charged and it still not work.

Try having someone recharge it under a vaccuum. Some places will reclaim the refrigerant you already have and only charge you for any amount you need to add beyond what you already had (if you had enough already they shouldnt charge for me refrigerant, unless they aren't honest).

Cost me $60 the first time I had mine done. Had a lead and had to redo all of it, second time was about $100.