I have a 1998 E320 Mercedes. I noticed my auxilliary fans were not working when I start the car and turn on the AC even when it is 95 degree outside. I checked the fans and they do work and bought a new control unit but it still does not come on. Are they suppoed to come on once I turn the AC on or does the cabin have to be a certain temperature. Is there anyhting else I need to be looking at?