Several problems possible. Control unit, happens but rare, low pressure switcch, in A/C pipe near firewall, faulty relay, also rare, or most common, a faulty compressor high temp sensor. It screws in to the back of the compressor, and interrupts power to the clutch when temp is high or sensor fails. The sensor runs about $50 at the dealer, but might be available elsewhere. Discharging the system is not required. It is a bit tricky to replace, as there is not much room to work. You disconect the wiring from the car harness, A/C clutch, remove the plastic insulator from 1 of the 2 wires, and slip a short 16mm box end wrench over the wiring and up to the sensor. Crack it loose and it usually spins out by hand. Sensor located on rear of the comp, about midway up, on the engine side of compressor. Try unplugging the sensor and conecting the car harness directly to the clutch, bypassing the sensor to verify if this is the problem.