Pick up compressor and make sure it doesn;t look like crap (well too much like crap). INspect pully for warpage/bent ends and while you've got it in your hand rotate the wheel/pully by hand and see if it rotates freely. If it comes to a sudden stop, makes whirring/grinding noises, promptly put down the compressor and judo chop shopkeeper on the neck for wasting your time. If it spins freely and no bearing noise is heard, check the compessor clutch, using a battery energise the clutch and it should engage pretty strong. If you get an A-OK on all of the above, youse got yourself a kabli in good nick.(y)