Jay Giron 11/30/2011The big fan turns on when the coolant has reach the max engine operating temperature.
The small one turns on when the a/c is on because it puts extra load to the engine so the small fan
helps to cool down the engine.
the coolant temperature sensor sends a signal to the ECM that powers the fans. The current first
travels Through a fuse and then the fan relay finally the relay powers the fans.