Driving today, and noticed little to no cooling. Smelled something burning when I stopped. Opened hood, and small amount of smoke from A/C clutch. Let it cool, and then started car. Clutch is trying to engage, but slipping.

How can I tell if the compressor is seizing up, or if it is the clutch?

Thanks for your help, in advance.

See if you can turn the inside part of the pulley. That's the part that is bolted to the compressor shaft.

The next check would be to remove the belt, energize the clutch, then turn the pulley quickly by hand and and see if it slips on the inner part.

I would think that if the compressor siezed yet the clutch was still good and tight, that it would have caused the belt to slip on the pulley.

Compressor turns.
Started car, clutch cycled on and off. After a few minutes, the clutch began to slip.
I noticed that the fan(electric) was not turning, so I turned my attention to that. As I was looking into that, the upper hose area of the radiator broke loose, shooting coolant everywhere. New problem: new radiator required!

So is the fan not turning causing the compressor to become too tight for the clutch to turn?

"...upper hose area of the radiator broke loose, shooting coolant everywhere..."

Although the problems seem to be mounting, you are actually quite lucky that the radiator neck broke when it did, vs out on the road like mine did. My wife called me and said "There's smoke [actually steam] coming out the front of the car and the engine is making a knocking noise."

I'm not sure if there is a correlation between the slipping A/C clutch and the fan non-op, unless there is a bad electrical connection somewhere that is flaky and doesn't allow enough current to either of the components when it gets hot. You could check for a voltage drop to the compressor when the slipping starts.

Check out these posts for some insight into how it all works particularly the part about the fuseable link:

http://www.brickboard.com/RWD/volvo/1431109/940/960/980/V90/S90/lets_stick_fan_now.html

http://www.brickboard.com/RWD/volvo/1431604/940/960/980/V90/S90/lets_stick_fan_now.html

Bought a new radiator.
Before doing anything, I turned ignition to KPII, and jumpered the leads to the fan thermostat switch mounted in the radiator. Relay clicked, and fan started right up.
So I turned to replacing the radiator. Wrong Radiator!! 6" too narrow. It needs to be about 28" total width. But it is definitely what NAPA shows as correct for this car.
Anyway, that delay caused me to check the thermostat switch. Hooked up a meter and put it in boiling water. Switch would not close.
Anybody know where I can get the fan thermostat switch and the correct radiator.