Cherokeelad

I have a 98 XJ modified, but not too heavily. I took it for its first long roadtrip and about 180 miles into my trip my temp gauges jumped from 212ish to 250 setting off the check gauges light. So I pull over and sit for a second to see what happens. I turn off my AC during this and the temp gauge goes back to normal. So I start going again, with the AC on and it happens again. I have a very well maintained jeep that never let's me down so I'm lost at this point. After a while I start thinking that darn AC is part of it. I drove the rest of the trip windows down no AC and it never happened again. Anyone got an idea what's going on with my rig? Any ideas would be great. Thanks!