I also own 98 S70 T5 and 95 850 T5. I had the same problem with both. There's a kind of thermal switch behind compressor. I bypassed that switch. 12VDC power goes through that switch to compressor clutch. Especially during hot days, A/C will get cold for awhile and then starts blowing hot air. Turn off A/C for a few minutes and turn it back on, cold air again. That switch is preventing clutch to engage. You will need super long needle nose plires and small hand to bypass that.
Good Luck.