I recently replaced the A/C compressor on my 98 Cherokee because the clutch would not engage. Put the new one on and it wouldn’t do anything. After messing with the relay, it will engage momentarily and disengage. It does this if I plug/unplug or wiggle the relay just right. I’ve cleaned up all the terminals with that making no difference. Any suggestions as to what it might be? Loose connection in fuse box?

 

The computer provides the ground path for the AC clutch. Maybe clean your ground points (lots of searchable topics on this). You could also see if your refrigerant pressure is too low or too high. The low and high pressure switches will inhibit the ECU from sending that ground path.