PURPOSE: To prevent the occurrence of the lock state and the overload state of a compressor and to prevent the occurrence of failure in operation of a compressor and the damage and seizure thereof by a method wherein when, during the restarting of the compressor from a stop, a difference between the high and the low pressure of a refrigerating cycle exceeds a given value, the starting of the compressor is blocked.

CONSTITUTION: When a 4-way valve 2 causes a heat exchanger 3 on the heat source side to form a condenser, a vaporizing action is performed by a heat exchanger 5 on the utilization side, and a load is cooled. When the 4-way valve 2 is switched, the heat exchanger 3 on the heat source side forms a vaporizer, a vaporizing action is effected by the heat exchanger 5 on the utilization side to perform heating of a load. A pressure sensor 6 detects a pressure, e.g. the suction pressure of a compressor 1, on the low pressure side of a refrigerating cycle, and a pressure sensor 7 detects a pressure, e.g., the delivery pressure of the compressor 1, on the high pressure side of the freezing cycle. When a pressure difference between a pressure 7 on the high pressure side and a pressure 6 on the low pressure side exceeds a given value, the starting of running of the compressor is blocked.