Today on my 2008 Mazda 3 when we were driving in town the temperature started climbing toward overheat. The radiator fan isn't coming on. I turned the AC on and the fan came on and cooled it back down. I turned the AC off and the temp started climbing again. The only work that has been done recently is the alternator was changed 3 weeks ago. Any ideas?

 

The fan started working without ac on. Will keep checking to make sure it's not intermittent.