Outdoor unit, indoor unit, and air conditioning system

An air conditioning system comprising:

• a refrigerant circuit that performs a refrigeration cycle;
• an outdoor unit and indoor units connected in parallel to the outdoor unit, wherein the outdoor unit comprises a first control valve;
• and
• a control unit configured to cause the air conditioning system to operate in a first control mode or a second control mode based on presence or absence of a valve unit that comprises a second control valve and that is disposed between the indoor units and the outdoor unit in the air conditioning system, wherein
• in a case where the valve unit is absent from the air conditioning system, the control unit causes the air conditioning system to operate in the first control mode in which a pressure of a refrigerant to be supplied to the indoor units is adjusted by controlling the first control valve, and
• in a case where the valve unit is present in the air conditioning system, the control unit causes the air conditioning system to operate in the second control mode in which a pressure of a refrigerant to be supplied to the indoor units is adjusted by controlling the second control valve.