Every A/C system dreams of being a "constant pressure" system. Unfortunately, the combination of engine speed, outside temperature, condenser airflow, cabin temperature, and recirculation, all work against every A/C system.

What is it about the 960 pump design that makes it different than the standard compressor? Do the later models have constantly running compressors? I guess I'm confused about how different those systems are. I don't get to work on them that much, but the amount of A/C advice I give out on them would be tempered by finding out that they were radically different in some way, shape or form.

If they are a cycling clutch/orifice tube system like all the rest of the 900 series cars, however, they are no more a 'constant pressure' system than any other Volvo 900. The pressure is controlled by the same factors, but the output temperature acts as a trigger to moderate the vent and cabin temp.
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Chris Herbst, near Chicago.