An outdoor unit, an air conditioning system, and a control method. The outdoor unit comprises a first connection tube (1) and a second connection tube (2) communicating with an indoor unit, and further comprises a compressor, two heat exchangers (4), two directional valves (5), and two throttling devices (6). One of the two heat exchangers (4) communicates with one of the two directional valves (5). In the outdoor unit, the air conditioning system, and the control method, two heat exchangers (4) are provided, such that a portion of a high-temperature refrigerant enters the indoor unit during a process in which the air conditioner outdoor unit performs defrosting, and the indoor unit does not stop running and continues generating heat while the outdoor unit performs defrosting, thereby ensuring heat generation capacity of the units and maintaining the indoor outlet air temperature and user comfort; in addition, when heat generation is performed at high temperatures or cooling is performed at low temperatures, only a first heat exchanger (41) operates, and an appropriate adjustment is performed on system pressure, thereby ensuring reliability of the units and user comfort.