I posted about this earlier but gave tons of detail. Here's a much abridged version in case the long explanation kept people from reading the whole thing. I had a pulley that was wobbling because the bearing had gone bad. I put a new pulley on the compressor and it was nice and snug going on - had to use a rubber mallet to gently tap it onto the compressor, but I noticed once I got it on that there was still a little wobble in it, and I'm pretty sure it's not the bearing. When I put it all back together, the AC worked but as soon as the compressor disengaged the clutch, it started making the grinding sound that had alerted me to the problem in the first place, and smoke started coming off of the pulley and clutch. Any ideas?