I recently developed a noisy bearing in the A/C compressor on my 2000 TJ 4.0. With the A/C switched on, it got quieter-a dead give-a-way of the source.
Beside the fact that NO shop (including a local independent Jeep specialty shop) would change just the bearing (every one wanted to replace the compressor for about $1000+ an A/C recharge), I had much trouble finding the correct bearing. No auto parts store obtained the correct one (we sent several back).
Jeep sells only the entire pulley w/ the bearing already pressed in it for just over $200. They say the bearing is not available as a separate part.
It took many many inquiries, but I finally found the right bearing from a Koyo distributor (OEM supplier) in Memphis for $14.45 plus shipping. Apparently Koyo is the ONLY bearing company who offers this size, at least in the USA.
The old one came out with a few taps, and the new one went in as easily, so DO NOT let a dealer/shop talk you into a more expensive solution.
BTW, you do have to pull the radiator to get at it (no big deal since I was replacing mine at the same time anyway because of the plastic-to-aluminum leak), but after that it's a piece of cake. You don't touch the compressor itself, and no recharge is necessary, of course.
It goes w/o saying that you should probably change the tensioner and idler bearings, and maybe the serpentine belt at the same time (about $15 each as well). If you have pver 100K mi, the water pump is a good idea as well.