I've noticed the AC wasn't very cold the last time in the car, today it quit blowing any cool air at all and I noticed the compressor will not come on either when the AC is turned on, nor do the rpms drop.
I know there is a pressure sensor/switch in the AC line, so when pressure is low does it keep the compressor from running?

I'm guessing its a safety catch so you don't ruin the compressor running it without any R134A in it.
Thanks

 

Yeah the compressor won't run with out freon. If you look on your AC lines there is a weird little sensor and that is what reads your freon. I remember in Auto mechanics class we refilled a car and we had to put a paper clip in the plug in on the sensor so the compressor would come on and suck the freon in.