Coolant Fan Relay. I had to replace mine this summer. Very common for those to go out on the WJ's. Basically your coolant fan is not speeding up when the engine is getting warm and this is really common when you turn on the A/C. Not sure if there was a write up on http://www.wjjeeps.com but it is prety easy fix once you do it the first time. Here is the link on how to get to the relay. http://rigs.corequipment.com/cebby_WJsite/cooling.htm#relay
Kind of a pain the first time you replace it, but after you cut the hole, it is easy if you ever have to do it again. It is possible if it was replaced before, the hole is already cut. The relay is about $40-50 at the auto parts stores. The first one I got only lasted about 2 weeks and stopped working. Got another one and it has been working since. PM me if you have any more issues with the relay.