PURPOSE: To enable a high freezing capability to be outputted within a lower temperature range by a method wherein when a freezer is started to operate, a discharging pressure of a compressor is restricted low, an over-load operation of the compressor is prevented, a refrigerant condensing state is promoted and even after a pressure in the freezer is reduced, a sufficient amount of refrigerant is circulated.
CONSTITUTION: When an operation is started, the first opening or closing valve 15 and the second opening or closing valve 16 are opened, a bypass flow passage for refrigerant is generated and in concurrent with this operation, the first tank 13 and the second tank 14 are kept under a discharging pressure, the refrigerant is stored to restrict the discharging pressure of the compressor low. Then, the second opening or closing valve 16 is closed, the bypassing flow of the refrigerant is stopped and then the first opening or closing valve 15 is closed and the second opening or closing valve 16 is opened. The refrigerant in the second tank 14 passes through a flow rate metering mechanism 17 in reference to a pressure difference between a discharging pressure and a suction pressure, gradually moves to a compressor suction side refrigerant pipe 12 and the refrigerant is circulated to the heat exchanger system by the compressor 1. At this time, in order to prevent a compressor discharging pressure from being rapidly increased, the first tank 13 is operated as a pressure damping tank.