Maybe the pressure is up to par... but could the actual liquid r134 be low? I have heard somewhere that can happen if not recharged right. Also something about too much or too little liquid r134 and it won't cool properly. I would go and have someone that knows what they're doing and knows volvo exacuate the system and put in the correct amounts.

Another thought would be to inspect the condenser in front of the radiator and make sure it isn't clogged with bugs, dirt, etc.

If you know for sure that everything is 'right'... then I'd suggest getting your car's windows tinted as that helps keep the car's interior cooler. You don't need to get dark tint to feel the difference either.
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'94 855 5spd 'Drew' 203,000 Miles -Currently laid up getting a good internal cleaning and tomorrow a nice used head, new wires, seals and stuff-