A unitary air conditioning system comprises an outdoor unit including a compressor for compressing refrigerant, an outdoor heat exchanger for heat exchange of refrigerant, and an expander connected to the outdoor heat exchanger, for expanding refrigerant; a duct installed in each zone of a building; a plurality of central blower units, each unit having a heat exchanger connected to the outdoor unit by a refrigerant pipe and a blower for supplying the air heat-exchanged by the heat exchanger to the duct; and a cooling/heating control unit for selectively distributing a refrigerant from the outdoor unit toward the heat exchangers of the plurality of central blower units and controlling cooling or heating operation for each zone of the building. Accordingly, the plurality of blower units are systematically operated according to a load of each zone inside the building, so that the cooling or heating operation can be effectively performed on each zone.