well... first thing to check would be to see if there's actually refridgerant in the system. There's two pressure taps available underhood, one on one of the lines comming back from the car, the thick one. This is the low pressure side tap. There is another one right by the drier infront of the ac condenser.
Having a set of gagues would be the best way to see if everything's healthy, but a simple pressing of the valve in the middle quickly to see if anything tries to come out would probably be sufficient.
Unless it's been retrofitted, you're running R-12. You should retrofit if it is.
The connectors on the pressure taps will have adapters already on them if the system has been retrofitted.
If there's pressure in the lines, next check all the wire connections to the compressor. If they're all plugged in firmly, go turn on the a/c in the car and watch to see if the clutch engages on the compressor. if it doesn't engage, pull the connector off and check to see that the proper voltages are comming across when the a/c is turned on.
If they are, then the problem is most likely a dead compressor clutch. Go get a used compressor from a junkyard for cheap.
If they aren't then you will have to chase down either a wiring problem or a problem with the a/c controller itself.
NOW, if there WASN'T pressure in the lines, there is even more work, because this means there was probably a leak somewhere. What you would normally do here is get some leak indicator dye and a r-134a retrofit kit, and charge the system with r-134a with the dye added in.
To see this dye, you need a blacklight and the yellow tinted glasses. Once you locate the source of the leak, you can attempt to fix that part. After these repairs, charge the system, and see if it works. If not... go do the stuff that I listed above for if you HAVE pressure in the lines.
Good Luck. 8)
