An air conditioning system for a vehicle is provided. The system includes a cooling duct and a heating duct provided as spaces partitioned by a partition wall and an evaporator core and an inner condenser disposed respectively in the cooling and heating ducts. An outer condenser is connected to the inner condenser and the evaporator core via one refrigerant passage. An air volume regulation door is disposed upstream of the evaporator core and the inner condenser in an air flow direction, and a common blower is disposed at one side of the cooling and heating ducts to simultaneously form an air flow in the cooling and heating ducts.