An air conditioner system, comprising a compressor , an indoor heat exchanger , a first throttling device , and an outdoor heat exchanger connected in series in a main loop, wherein a heat exchanger is further disposed in the main loop, one side of the heat exchanger being connected with a first pipeline (M) between the first throttling device and the indoor heat exchanger , and an other side of the heat exchanger being connected with a second pipeline (N) between the first throttling device and the outdoor heat exchanger , so that a refrigerant passing through the first pipeline and a refrigerant passing through the second pipeline exchange heat in the heat exchanger, wherein the first pipeline (M) passes through one side of the heat exchanger, and the second pipeline (N) passes through the other side of the heat exchanger , wherein the air conditioner system further comprises a mode switching device being a four-way valve (Q), characterized in that a bypass defrosting loop (P) is disposed between the compressor and the outdoor heat exchanger, being configured to defrost the outdoor heat exchanger in a heating process of the air conditioner system, wherein a second throttling device is further disposed in the main loop, and is located in a zone of the first pipeline between the heat exchanger and the indoor heat exchanger, and the mode switching device is configured to switch the air conditioner system between a cooling mode where the first throttling device is in a full open state and the second throttling device is configured to throttle the refrigerant, and a heating mode where the second throttling device is in a full open state and the first throttling device is configured to throttle the refrigerant. wherein a heat exchanger is further disposed in the main loop, one side of the heat exchanger being connected with a first pipeline (M) between the first throttling device and the indoor heat exchanger , and an other side of the heat exchanger being connected with a second pipeline (N) between the first throttling device and the outdoor heat exchanger , so that a refrigerant passing through the first pipeline and a refrigerant passing through the second pipeline exchange heat in the heat exchanger, wherein the first pipeline (M) passes through one side of the heat exchanger, and the second pipeline (N) passes through the other side of the heat exchanger , wherein the air conditioner system further comprises a mode switching device being a four-way valve (Q), characterized in that a bypass defrosting loop (P) is disposed between the compressor and the outdoor heat exchanger, being configured to defrost the outdoor heat exchanger in a heating process of the air conditioner system, wherein a second throttling device is further disposed in the main loop, and is located in a zone of the first pipeline between the heat exchanger and the indoor heat exchanger, and the mode switching device is configured to switch the air conditioner system between a cooling mode where the first throttling device is in a full open state and the second throttling device is configured to throttle the refrigerant, and a heating mode where the second throttling device is in a full open state and the first throttling device is configured to throttle the refrigerant. <EOS>