In an automobile the compressor is driven by a pulley on the engine 's crankshaft , with both using electric motors for air circulation .
In an automobile , the compressor is driven by a belt over a pulley , the belt being driven by the engine 's crankshaft ( similar to the driving of the pulleys for the alternator , power steering , etc. ) . Whether in a car or building , both use electric fan motors for air circulation .