Not an unusual question (one that I had, too, when I first got a '93 like yours). After all, a fan in front of the radiator should have something to do with coolant temperature or A/C function -- and preferrably both!

But a look at Volvo's "green" Wiring Diagram book reveals that the control of that fan is solely by a pressure-sensitive switch, called a pressostat, on the A/C line located on a junction seen just underneath the radiator's return (lower) hose. The relay controling the fan (next to the black, electric junction box on the drivers-side fender) is also powered through the A/C relay; so you have two levels of control, in that the fan cannot work unless the A/C is switched on, and then again only if the A/C line pressure is too high. Nothing about coolant temperature at all.

Bottom line, the fan only comes on when the A/C is working hard, which (if you car is in good condition, viz. adequate refridgerant level, good fan clutch, etc.) is only rarely. Someone on this list in an earlier article did offer that he deliberately jumpered the plug into the pressostat so that the fan works continuously whenever the A/C is on -- he said his A/C works better, because he lives in Phoenix, AZ (as I recall) and needs the extra help all the time.

To test your fan and the relay, though, all you have to do is temporarily remove the plug from the aforementioned pressostat and use a paper clip to jumper across its contacts: if the A/C is running, the fan should start right away when your paper clip closes the circuit.

Regards,