An air conditioning system comprises: a motor that rotates a rotary shaft to which a compressor and an expansion device are connected; an expansion valve; a water separating device that separates water in first air that has been expanded with the expansion valve; and a hygrometer that measures the humidity in the first air before the same flows to the compressor. The air conditioning system further comprises a controlling device. The controlling device controls the motor speed and the degree that the expansion valve is opened on the basis of the measurement results of the hygrometer so that the humidity of the first air in the expansion device is less than 100%.
