Fan Module : This is the module that controls fan motors on some models of cars and trucks. A vehicle with a fan module uses the module to turn a fan on high, low or off in most systems. Some fan modules control the engine and auto air conditioning (AC) fan motor as well. A bad fan module can reduce auto air conditoning (AC) performance and or overheat the engine. Fan modules can burn up with a bad fan motor that draws too much DC amps.