Radiator fans

When are the radiator fans suppose to run? All the time the motor is running, when the AC is on or/and when the temp reaches a certain degree?
My daughters 2000 concord seems to run all the time. I have just replaced the fan assembly, frame and fans, due to a broke fan blade from a previous accident, I suppose.

They are supposed to only come on when the engine is hottest, I think usually when the temp goes above 180' if your in a hot climate it may be 'all the time'. When your driving on the freeway the fans can usually stop with the air flow into the engine, at stop and go traffic with the AC on the fans are going to be running.