One word of caution--with AC systems, there is such a thing as TOO MUCH refrigerant. EVERY YEAR on the various Jeep forums, some poor sucker keeps adding refrigerant to the system WAY PAST the allowable limit, and winds up hydrolocking his compressor and REALLY trashing the system.
If you cannot get it to run with the "DIY" approach suggested previously, I STRONGLY suggest you pay a pro to at least DIAGNOSE your problems, and then fix whatever is "bad" according to that diagnosis, and then pay the pro to evacuate/fill the system correctly.
AC systems are sensitive to being filled properly, and can get REALLY screwed up by not following proper procedures and using proper tools.
I don't own an XJ any longer, but I still think they are the best of all the Jeep products ever made. My XJ was my favorite vehicle in my 50+ years of driving.
So...I stick around and give advice.