A multi-air conditioner for cooling and heating, the multi-air conditioner comprising: at least one indoor unit (B) installed in a room, that comprises an indoor heat exchanger (B1, B2) and an indoor expansion valve ; an outdoor unit (A) connected to the indoor unit (B) via a refrigerant pipeline , that comprises an outdoor heat exchanger (A1, A2), a plurality of compressors , an outdoor expansion valve , and a four-way valve ; and a dedicated outdoor air ventilation unit (C) connected to the indoor unit (B) and the outdoor unit (A) via the refrigerant pipeline , that is configured to dehumidify and ventilate outdoor air and supply the outdoor air to the room, wherein the outdoor unit (A) comprises: a first compressor ; a second compressor ; a compressor valve configured to connect the second compressor both in series and parallel to the first compressor ; whereby the compressor valve is connected between the outlet side of the first compressor and an inlet side of the second compressor , and is configured to connect or disconnect the first compressor and the second compressor , wherein the outdoor unit (A) is configured to provide a refrigerant to both the dedicated outdoor air ventilation unit (C) and the indoor unit (B), whereby the compressor valve is configured to control the compression capacity depending on an operation mode of the dedicated outdoor air ventilation unit (C) and the indoor unit (B). at least one indoor unit (B) installed in a room, that comprises an indoor heat exchanger (B1, B2) and an indoor expansion valve ; an outdoor unit (A) connected to the indoor unit (B) via a refrigerant pipeline , that comprises an outdoor heat exchanger (A1, A2), a plurality of compressors , an outdoor expansion valve , and a four-way valve ; and a dedicated outdoor air ventilation unit (C) connected to the indoor unit (B) and the outdoor unit (A) via the refrigerant pipeline , that is configured to dehumidify and ventilate outdoor air and supply the outdoor air to the room, wherein the outdoor unit (A) comprises: a first compressor ; a second compressor ; a compressor valve configured to connect the second compressor both in series and parallel to the first compressor ; whereby the compressor valve is connected between the outlet side of the first compressor and an inlet side of the second compressor , and is configured to connect or disconnect the first compressor and the second compressor , wherein the outdoor unit (A) is configured to provide a refrigerant to both the dedicated outdoor air ventilation unit (C) and the indoor unit (B), whereby the compressor valve is configured to control the compression capacity depending on an operation mode of the dedicated outdoor air ventilation unit (C) and the indoor unit (B). a first compressor ; a second compressor ; a compressor valve configured to connect the second compressor both in series and parallel to the first compressor ; whereby the compressor valve is connected between the outlet side of the first compressor and an inlet side of the second compressor , and is configured to connect or disconnect the first compressor and the second compressor , wherein the outdoor unit (A) is configured to provide a refrigerant to both the dedicated outdoor air ventilation unit (C) and the indoor unit (B), whereby the compressor valve is configured to control the compression capacity depending on an operation mode of the dedicated outdoor air ventilation unit (C) and the indoor unit (B). <EOS>