How can i tell if compressor is bad

In the worst case the shaft will be frozen and when the compressor clutch engages, your serpetine belt will smoke and fall off. Before that, if you have the proper Freon pressure and the compressor clutch engages, it will make a noise like loose marbles scrapping inside a cylinder.

There is suppose to be oil in the compressor, a certain weight like motoroil differs, get the right one. There are cans of Freon which have an oil charge in them. You add it to the low pressure side of the system just like regular Freon. Sometimes you can get lucky and add it and the noise will go away and there is no damage. Other times the parts are pitted and the oil will lube them up and its too late.

If your A/C is not putting out and not making noise, then it is something else like a simple recharge or fixing a leak.