Jeep Liberty Forum : “AIr conditioner pump works sporaticly why? Relay?”

It sounds like the clutch could be going bad.

Did you just have it charged?  It might have too much pressure in the system, and when the compressor engages, it kicks off due to having too high of pressure.  I've done this before.  If that is applicable, you will need to take it to a shop and have some of the refrigerant/oil bled out, as it should not be released into the atmosphere and must be collected.