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.
1992 XJ 2" lift -- RIP
2000 XJ 3" lift -- Australian Ford Big Brakes up front, rock rails, ZJ rear discs (with WORKING parking brake), C4x4 rear bumper/tire carrier, Hella H4 headlights, IPF driving lights, OEM skid plates, OME springs/shocks, JKS LCA's, JKS Sway Bar links.