Vehicle air-conditioning system

The present invention balances power consumption reduction and a cooling in a vehicle air-conditioning system having a compressor (1) selectively driven by a vehicle engine (20) or a motor (21) while the compressor (1) is driven by the motor (21). At least one of a capacity of a blower (7) and a capacity of a compressor (1) arranged in a refrigeration cycle R while the compressor (1) being driven by a motor (21) is reduced in comparison to the capacity of the blower (7) and the capacity of the compressor (1) while the compressor (1) being driven by a vehicle engine (20). Furthermore, while a cooling heat load of an evaporator (5) is greater than a predetermined value, the capacity of the compressor (1) is first reduced prior to reducing the capacity of the blower (7).