Shouldnt' be too hard. I've installed A/C in my YJ and the TJ is a bit easier. Performance wise, you'll feel the HP hit when it kicks in. It's not bad when you're cruising though. You might want to turn it off when you wind the engine up over 4000. On a 100+ degree day, it will pay for itself quickly. For best results you'll want a hardtop with full doors. You could also go with a halfcab/top. Having a full soft top will work but it won't be efficent at all.
There are only a few places that sell Jeep kits though.
www.jeepair.com, who I bought mine from,
www.ACkits.com and
www.collinsbrosjeep.com (they don't do TJ kits though). Keep in mind that all these kits use a non-oem compressor and an additional bracket that sits on the A/C mount. Why they don't use an OEM style compressor, I don't know. I piecemeal'ed my 'kit' so I could use an OEM compressor which made ordering a PITA but I've finally got it sorted. The reason for this was because I use a OBA and it requires another bracket and spacers for the OBA compressor. I didn't want to be stacking brackets on brackets when I didn't need to. If you want to go this route, I can tell you which parts I ordered.
The second part, you'll have to do is have the system vacuum'ed out for a minimum of 45 minutes (I do it overnight but that's not possible if you have a shop do it.) Then the system will need to be charged. The equipment is about $150-200 and the R134a cans are anywhere from $6-12 for a 1lbs can. You need two. A shop will charge around $125 for a vacuum and charge.
