Hello,
It sounds as if the vehicle is overheating on you occasionally. The electric cooling fan is designed to come on when the coolant/antifreeze reaches 215 degrees. The electric cooling fan is supposed to come on automatically whenever the A/C is as well. Some fans have two speeds as well. If the fan is not working at all or the highest speed is not working, the vehicle can overheat. Under normal driving conditions without the A/C on, it may be fine as long as you are moving and airflow is coming through the radiator. As far as the A/C quitting when this happens, there are two pressure switches for the A/C system. The pressures in the system may get too high due to the lack of airflow though the condensor assembly (in front of radiator). The switches are designed to shut-down compressor to prevent further damage. Several things to check for cooling fan problems. Fuses, relays, a/c or coolant switches, wiring, fan controller, or even a engine control module. Hope this helps and good luck.