You must remove the Compressor (Disconnect all wires from the compressor and un-bolt it) and then take the pulley off of the compressor(May require a pulley puller). Make sure Not to damage the electro magnet or the Pulley. I would recomend replacing the Entire compressor if the bearing has been bad for a while.
In order to replace the bearing in your GM air conditioning you are going to need a few mechanical tools. Once you have these tools you can take off and replace the bearing.
