An air conditioning system for a vehicle includes a hybrid compressor having a first compression mechanism driven by a drive source for driving the vehicle and a second compression mechanism driven by an electric motor, means for selecting a drive source, a means for detecting a refrigeration cycle condition, and means for estimating a power consumption of the compressor due to a selected drive source and a power consumption of the compressor due to a non-selected drive source in response to a value detected by the means for detecting a refrigeration cycle condition, when one drive source has been selected. Through this estimation, an preferred drive source may be selected in response to the condition of the refrigeration cycle or a thermal load.