REFRIGERATION CYCLE SYSTEM, HEAT SOURCE UNIT, AND REFRIGERATION CYCLE DEVICE

A refrigeration cycle system, a heat source unit, or a refrigeration cycle apparatus using a carbon dioxide refrigerant enables supply of a sufficient amount of a high-pressure refrigerant to a plurality of utilization heat exchangers. A refrigeration cycle system (1) using a carbon dioxide refrigerant includes: a heat source circuit (12) including a secondary-side compressor (21), a cascade heat exchanger (35), a secondary-side switching mechanism (22), and a suction flow path (23); a plurality of utilization circuits (13a, 13b, 13c) respectively including utilization-side heat exchanger (52a, 52b, 52c); a first communication pipe (8); a second communication pipe (9); a third communication pipe (7); a connection path (45); and a first on-off valve (46). The first communication pipe (8) and the first heat source pipe (28) connect the plurality of utilization-side heat exchangers (52a, 52b, 52c) and the secondary-side switching mechanism (22). The second communication pipe (9) and the second heat source pipe (29) connect the plurality of utilization-side heat exchangers (52a, 52b, 52c) and suction flow path (23). The third communication pipe (7), the fourth heat source pipe (26), and the fifth heat source pipe (27) connect the plurality of utilization-side heat exchangers (52a, 52b, 52c) and the cascade heat exchanger (35). The connection path (45) connects the first communication pipe (8) and the second communication pipe (9). The first on-off valve (46) switches between a state in which the first communication pipe (8) and the second communication pipe (9) connect and a state in which they do not connect.