The radiator fan control module controls when to turn the cooling fan on and off, based on readings received from the engine control module. There are various switches and sensors throughout the cooling system that determine when the fan initiates, based mainly on temperature readings. If the control unit is faulty, neither the cooling fan or the A/C fan will operate, which can cause an overheating condition. This is not likely to turn on a check engine light until the engine begins to overheat. Don't take a chance in ruining your engine and replace your faulty control module.