If they're being honest and they checked the high pressure output, then yes, the compressor should be good. This is IF the charge and replacement parts were all executed properly.

There was a good suggestion about the condenser. A clogged condenser is almost useless, and is a common problem (I often overlook it).

Also, if the heater valve check and the condenser inspection don't turn up anything unusual, it might be worth the money to have a cursory inspection done by a reputable A/C shop. I know of one A/C shop in my area that does fantastic work at about 1/2 price of others. There are usually a few great places like this in any major metropolitan area. Ask around a little bit, but first see if the other suggestions might shine some light on the situation.
--
Chris Herbst
1992 945, 71k
Volvo shop tech