The present invention relates to an air conditioning system and, more particularly, to an air conditioning system comprising, within a single air conditioning case: a cool air passage in which an evaporator is installed; a warm air passage in which a condenser is installed; an installation space portion in which air conditioner parts such as a compressor are installed; and an air discharge passage for discharging, to the outside, air unnecessary for cooling and heating, thereby enabling attachment and detachment inside a vehicle, and enabling use as a portable air conditioner as well as a vehicle air conditioner. In addition, as the system is capable of cooling and heating, a separate heater core or PTC heater for heating is not required, thereby the structure is simple, and the system is capable of controlling cooling and heating modes through a single operation door, thereby allowing the system to be miniaturized.