A feedback control logic system for commanding a particular air conditioning unit fan speed is driven by a pulse-width modulated signal from a control unit. The engine control unit decrements the pulse-width modulated signal to the air conditioning unit fan and allows the fan to run for a predetermined time. If a particular function, such as shutting off of an air conditioner pressure switch or other sensor, has not been achieved within the predetermined time, the engine control unit again decrements the pulse-width modulated signal.