Apparatus and method for controlling duty ratio for cooling fan associated motor of vehicle

A cooling fan which cools both an engine coolant radiator and an air conditioner refrigerant condenser is revolved by a motor whose duty ratio is controlled so that the sum (T1) of the torque (Ti1) required for a generator to drive the motor and the torque (Tc1) required to drive a compressor of the air conditioner is minimized while satisfying a control demand (X,Y) for a coolant temperature (Tw) and a refrigerant pressure (P).