98 Cherokee a/c compressor problems
 

I have a 1998 cherokee classic and when I turn the a/c on the compressor will turn over...sometimes but never consistently and it does not work long enough to blow cold. I have checked the r-134a level and it is full. I have also had it tested for leaks and there are not any leaks??? Could this be a bad relay? Is the compressor gone? Where do I start? Thanks
:wallbash: