Originally Posted by 8VETTE7

Factor set temps are both fans come on at low speed at 225 degrees and will go off when the temp drops below 219 degrees. If the engine temp rises to 235 degrees both fans switch from low speed mode to high speed mode. When the temp reaches 226 degrees the fans revert to low speed mode. All of this operation is out the window if the vehicle speed is greater than 35mph. Above 35mph the fans are commanded off irrespective of engine temp.

Additionally if the engine temp is greater than 185 degrees and you turn on the AC, both fans come on in low speed mode (again assuming the vehicles speed is less than 35mph) With AC on they will not go to high speed until the engine temp reaches 235.