why does my 07 navigator get hot only when the ac is on and I am stopped for a period of time but not while driving? can it be the fan clutch?

your thermostat is about to go out and is probably just sticking now or your water pump

Because when you're moving you have the benefit of air flowing through the radiator as opposed to only fan driven air when you're stopped. You just might need a regular radiator flush and filled back up with 50/50. Auto parts stores, even places like Walmart and Target sell these little antifreeze testers with like 4-5 colored balls inside a tube. You stick the tube in antifreeze and the amount of balls floating tell you what shape your coolant is in

http://www.carid.com/thexton/thexton-automotive-tools-35968751.html Actually Walmart has a better Prestone tester without the little balls. http://www.walmart.com/ip/Prestone-Antifreeze-Tester/16817506

Thanks for all replies. my heater is blowing hot so I figured the thermostat is open and working,I had recently added coolant, I have no electric fans, I put on a new serpentine belt and tension pulley,a friend suggested that the ac compressor may be dragging and causing it to heat up or it may be the fan clutch. thanks for all the help everyone.