If you can, just put a set of gauges across the compressor. If the compressor is compressing the refrigerant then it is fine. You should find the leak however. This may be a little harder to do. Do you know if leak detection dye was installed into the system? If not you may have to just try by soaping the joints. Most likely it is just one of the service valves. Are all the caps on the service valves? These are known to be trouble spots on any refrigeration system.
Good luck
