An air conditioning system 100, comprising: a compressor for compressing refrigerant; a condenser and for condensing the refrigerant discharged from the compressor; a first expansion device for throttling the refrigerant passed through the condenser; a second expansion device for throttling the refrigerant passed through the first expansion device; the air conditioning system further comprises: an injection valve for throttling the refrigerant bypassed between the first expansion device and the second expansion device and injecting into the compressor; and a control unit arranged to control the opening degree of the injection valve such that the ratio of a liquid refrigerant in the refrigerant injected into the compressor is less than a predetermined value; and an injection heat exchanger for performing heat exchange between the refrigerant passed through the injection valve and the refrigerant introduced into the second expansion device when the air conditioning system is in a heating operation, characterised in that the injection heat exchanger is installed at a base pan of an outdoor unit included in the air conditioning system, and disposed in parallel to the base pan, wherein the injection heat exchanger comprises a first refrigerant pipe for passing either the refrigerant passed through the injection valve or the refrigerant introduced into the second expansion device through and a second refrigerant pipe formed so as to cover the first refrigerant pipe and for passing the other refrigerant through, wherein the injection heat exchanger is formed in a loop shape by being bent multiple times, wherein an outdoor heat exchanger of the outdoor unit is disposed perpendicular to the base pan. a compressor for compressing refrigerant; a condenser and for condensing the refrigerant discharged from the compressor; a first expansion device for throttling the refrigerant passed through the condenser; a second expansion device for throttling the refrigerant passed through the first expansion device; the air conditioning system further comprises: an injection valve for throttling the refrigerant bypassed between the first expansion device and the second expansion device and injecting into the compressor; and a control unit arranged to control the opening degree of the injection valve such that the ratio of a liquid refrigerant in the refrigerant injected into the compressor is less than a predetermined value; and an injection heat exchanger for performing heat exchange between the refrigerant passed through the injection valve and the refrigerant introduced into the second expansion device when the air conditioning system is in a heating operation, characterised in that the injection heat exchanger is installed at a base pan of an outdoor unit included in the air conditioning system, and disposed in parallel to the base pan, wherein the injection heat exchanger comprises a first refrigerant pipe for passing either the refrigerant passed through the injection valve or the refrigerant introduced into the second expansion device through and a second refrigerant pipe formed so as to cover the first refrigerant pipe and for passing the other refrigerant through, wherein the injection heat exchanger is formed in a loop shape by being bent multiple times, wherein an outdoor heat exchanger of the outdoor unit is disposed perpendicular to the base pan. an injection valve for throttling the refrigerant bypassed between the first expansion device and the second expansion device and injecting into the compressor; and a control unit arranged to control the opening degree of the injection valve such that the ratio of a liquid refrigerant in the refrigerant injected into the compressor is less than a predetermined value; and an injection heat exchanger for performing heat exchange between the refrigerant passed through the injection valve and the refrigerant introduced into the second expansion device when the air conditioning system is in a heating operation, characterised in that the injection heat exchanger is installed at a base pan of an outdoor unit included in the air conditioning system, and disposed in parallel to the base pan, wherein the injection heat exchanger comprises a first refrigerant pipe for passing either the refrigerant passed through the injection valve or the refrigerant introduced into the second expansion device through and a second refrigerant pipe formed so as to cover the first refrigerant pipe and for passing the other refrigerant through, wherein the injection heat exchanger is formed in a loop shape by being bent multiple times, wherein an outdoor heat exchanger of the outdoor unit is disposed perpendicular to the base pan.