1990 Trooper w/ 2.8 v6. When a/c is on, and idle is under 1000 rpms, the compressor spins and sounds just like ICE IN A BLENDER. When rpms go over about 1000, clutch engages and noise goes away. A/C blows cold. I know that the previous owner changed the compressor, and it is prob. converted to r134. If I can get away with just changing the compressor's clutch, I'd be saving money and time. If anyone out there has experienced the same phenomenon, please let me know. Thanks!