A variable frequency control module includes a temperature detecting unit outputting a detecting signal corresponding to ambient temperature detected thereby, an operating unit operable so as to output an input signal corresponding to a target temperature, and a processing unit receiving the detecting signal and the input signal from the temperature detecting unit and the operating unit., and outputting a control signal corresponding to a difference between the ambient temperature and the target temperature based on the detecting signal and the input signal. An encoding unit receives the control signal from the processing unit, encodes the control signal into an encoded signal, and outputs the encoded signal to a frequency converting unit that outputs a driving signal having a frequency corresponding to the encoded signal to an AC compressor so that an AC compressor is operated at a rotary speed based on the driving signal.