after about 5-6 times of cycling on and off my compressor clutch stops engaging. the way I usually get it to cycle on is to rev the engine up to about 5000rpm and hold it for a second and it will engage. the freon pressure is fine, it blows freezing cold as soon as the compressor engages. I replaced the thermal control amp. the system cycles on and the engine rpm's increase to compensate for the drag of the compressor, but it just stops engaging. I can't figure out what revving the engine up has to do with anything.