2002 Nissan Quest Engine runs HOt intermittently

Recently may vehicle has been running very hot, coolant needle on H. This happens very intermittently (about 1 or 2X per week). Can happen day or night regardless of outdoor temps. Normally the temp gauge stays in the middle. I typically notice the problem when my AC starts blowing out warm air. When that happens I shut down the AC and within a few minutes the gauge goes back to the middle and everything is fine. I did notice that the cooling fan kicks on and stays on until the temp goes back down, so I dont think that is the problem. I have no leaks of coolant and the reservoir is filled.
Any thought?
Thanks,
Ed