Outdoor unit and air-conditioning apparatus

An outdoor unit comprising:

• a compressor configured to suck refrigerant, compress the sucked refrigerant, and discharge the compressed refrigerant;
• first and second refrigerant flow switching four-way valves configured to switch a flow passage for the refrigerant between a flow passage for a cooling operation and a flow passage for a heating operation;
• a plurality of heat-source-side heat exchangers, each configured to cause heat exchange to be performed between the refrigerant and external fluid;
• a plurality of heat-source-side backflow prevention check valves and a plurality of connection pipes that are included in a flow passage for the refrigerant in which an outlet from which the refrigerant flows out to an outside region and an inlet into which the refrigerant flows from the outside region are unchanged regardless of which of the cooling operation and the heating operation is performed;
• first and second flow-passage-pipe backflow prevention check valves, respectively provided on first and second flow passage pipes, configured to prevent during the cooling operation backflow of the refrigerant to the inlet from being caused by switching of the first and second refrigerant flow switching four-way valves;
• a third flow passage pipe through which part of the refrigerant having flowed from the inlet passes during the cooling operation;
• a third refrigerant flow switching four-way valve provided at the third flow passage pipe and configured to control passage of the refrigerant;
• a third flow-passage-pipe backflow prevention check valve provided at the third flow passage pipe and configured to prevent during the cooling operation backflow of the refrigerant to the inlet from being caused by switching by the second of the third refrigerant flow switching four-way valve;
• an accumulator, provided on a suction side of the compressor, that stores surplus refrigerant and supplies refrigerant to the compressor;
• and
• a controller configured to control the switching of the first, second, and third refrigerant flow switching four-way valves, wherein:
• during the cooling operation, refrigerant entering the outdoor unit through the inlet is divided into a first branch to the first and second flow passage pipes and into a second branch to the third flow passage pipe,
• during the cooling operation, the first and second switching four-way valves pass refrigerant divided into the first branch to the accumulator and further pass refrigerant flowing out of a discharge side of the compressor to the plurality of heat exchangers, and
• during the cooling operation, the third switching four-way valve passes refrigerant divided into the second branch to the accumulator.