I've had similar problems with mine. My a/c would just cut on and off prematurely resulting in constant shifts in rpms going up to the 1500-2100 range. So far I've found three common problems with a/c's which are hose leaks, compressors, and clutches. Now if your a/c can still cool the air and it's just running up the rpms it's probably a clutch problem.
However this is just what I've found online, I'm waiting for my service manual to look it up so I can't really say.