To test the compressor, do the following:
1. Rent A/C gauges from Auto Zone and connect to the low and high pressure fittings. See what the pressure is in the system. The static pressure with the engine not running should be at least 50 psi for a properly charged system.
2. Is system is charged, check the A/C switch, A/C thermostat switch, and the A/C relay. Any one of those may cause the clutch to not operate. Then, is no problem found here, check the supply voltage on the compressor clutch wires. If 12 V is present, and clutch still does not engage, check the resistance of the clutch with an ohmmeter. You should see about 2-5 ohms if the clutch is good. A burnt out clutch will have infinite resistance (=no continuity in windings).