2002 Mazda 626 CUTTING OFF

Three times in the last two weeks my car has shut off and would not restart right away. All three times I was sitting in parking lots with the engine idling and the ac running. I sat at idle approximately 10 to 15 minutes each time. First time car would'nt start for approximatelly 2 hours, then started. Second time car would start after approximately 3 hours and had it towed to a mechanic who waited two days to work on car, where it started. Third time car would'nt start for 40 minutes.