a/c problem

The clutch on the ac motor (the one that has a belt to it) is acting weird on my 4.3 97 jimmy --I say clutch because sometimes it spins sometimes not-- now I know that is what a clutch is supposed to do -- however it cycles about every 45-60 seconds. What do I need to do to fix this-- I hope it is just as simple as refueling the freon-- but I doubt it!!

I have owned this truck for 10 years and I dont wannna lose the air : )-- Thank you for your help!!

Low R134a can do that.
Put a high and low AC gauge set on.
Post back pressure readings at idle and at 2K with compresser running.