An air conditioning system for a vehicle includes a compressor. The vehicle includes a first drive source and the compressor includes a second drive source. The compressor is driven by the first drive source or the second drive source, or a combination thereof, and the second drive source includes an electrical power supply. The air conditioning system also includes a controller for selecting between the first drive source and the second drive source, such that when the compressor is active, the first drive source drives the compressor except when the vehicle is operating in a predetermined mode, a voltage of the electrical power supply is greater than or equal to a minimum electrical power supply voltage, and an amount of electric power consumed by the second drive source is less than a maximum electric power. For example, the predetermined mode may be an idle-stop mode.