Controller of Air Conditioning Apparatus, Outdoor Unit, Branch Unit, Heat Source Unit, and Air Conditioning Apparatus

A controller that controls an air conditioning apparatus configured to operate in operation modes including a heating mode and a defrosting mode, the air conditioning apparatus comprising:

• a compressor configured to compress a first heat medium;
• a first heat exchanger configured to perform heat exchange between the first heat medium and outdoor air;
• a second heat exchanger configured to perform heat exchange between the first heat medium and a second heat medium;
• a plurality of third heat exchangers each configured to perform heat exchange between the second heat medium and indoor air;
• a plurality of flow rate control valves each configured to control a flow rate of the second heat medium flowing through a corresponding one of the plurality of third heat exchangers;
• and
• a pump configured to circulate the second heat medium between the plurality of third heat exchangers and the second heat exchanger, wherein
• in the heating mode, the controller is configured to open a flow rate control valve corresponding to a heat exchanger that is being requested to perform air conditioning of the plurality of third heat exchangers, and to close a flow rate control valve corresponding to a heat exchanger that is not being requested to perform air conditioning of the plurality of third heat exchangers, and
• in the defrosting mode, when a temperature of the second heat medium is lower than a first determination temperature, the controller is configured to open a flow rate control valve corresponding to at least one of the heat exchangers that are not being requested to perform air conditioning, the at least one of the heat exchangers being assigned a higher priority than a remaining heat exchanger that is not being requested to perform air conditioning.