Low Pressure Cut-off switch is the first thing that comes to mind. The Last generation XJ's got real shotty Evaporators and just about every one of them leaks. My 99 is leaking, my boss's 98 is leaking, and chances are yours is too. If this is the case, you've probably lost most of your freon, therefore tripping the low pressure cut-off switch. This stops the compressor from running and causing damage to it. You might could get away with just adding some freon to it and hoping it comes back, But if you have the resources, i'd pull a vacuum on it and get every bit of freon out and start over from new. Pulling a vacuum will also determine how big of leak you have.
If you want to fix this problem for good by replacing the evaporator, there is no easy way to do it. The Evaporator is behind the dash, and the entire dash has to come apart. About a $700 and an all day job if you take it to the dealer to get it done, or a heck of a lot cheaper and still atleast an entire day to kill tearing apart your Jeep if you choose to doit your self. Me, I just check mine on a monthly basis during the summer and especially at the beginning of the summer, after its sat all winter. Usually on mine one good top off at the beginning of the summer is enough to get me through.
Do a search for "Evaporator" and there are litterally hundreds of posts on it.
