An air-conditioning system for conditioning air in a vehicle passenger compartment is configured to operate in a cooling system mode for cooling air to be supplied to the passenger compartment and in a heat pump mode for heating the same, and to operate in a reheating mode. The air-conditioning system includes a housing having a first flow channel and a second flow channel for guiding air to an air distribution system having discharge ports communicating with the passenger compartment, and a refrigerant circulation system having at least two heat exchangers. In this case, the first heat exchanger that operates as an evaporator regardless of operating modes is disposed in the first flow channel, and the second heat exchanger that operates as a condenser/gas cooler regardless of operating modes is disposed in the second flow channel.