An air conditioner, comprising an outdoor unit used exclusively for a multiple system having a capacity−controllable compressor mounted thereon, a refrigerant flow control unit connected to the outdoor unit, and a single or a plurality of indoor units used exclusively for one−to−one system connected to the refrigerant flow control unit, the outdoor unit and the indoor unit further comprising no restrictor, the refrigerant flow control unit further comprising communication means corresponding to the indoor units and restrictors corresponding to the indoor units and a communication means corresponding to the outdoor unit, wherein the refrigerant flow control unit collects the information on operation of the indoor units and regulates the restrictors to controllably distribute a proper amount of refrigerant flow to the indoor units and the communication means controls the compressor operating frequency of the outdoor unit for supplying the required refrigerant flow to the indoor units.
