PURPOSE: To maintain the refrigerating cycle at high efficient level and realize the effective cold storage by a method wherein the ices yielded to the predetermined thickness at heat exchangers during cooling are molten off by changing-over the cycle of the system to the heating cycle for the heating operation.

CONSTITUTION: At the period of cold storage in cooling, the refrigerant circuit consists of a compressor 1, a four-way valve 2, a radiator 3, an expansion valve 5, each of the heat exchanger 7 within a heat- and cold-storage tank 6, the four-way valve 2 and the compressor 1. When the ices yield over each surface of the heat exchangers 7 to the thickness of the order indicated as the frozen zone 15 in the attached sketch, the yielded ices are sensed by a sensing unit 13 to reverse the four-way valve 2 to change over the cycle of the system to the heating cycle, in which each of the heat exchangers 7 is served as condenser and heat to melt off the ice on the surface. Thus, the molten-off ices, aparting from the heat exchangers 7, float up to gather to the upper part of the tank 6. And the cylce of the system starts the cooling operation again, being changed-over to the refrigeranting cycle to start to cool the water, because the lower is the temperature of the water below 4°C, the smaller is the specific weight of the water, resulting in gathering the water having comparatively high temperature within the tank 6 to the neighborhood of the heat exchangers 7 in the lower part of the heat- and cold-storage tank 6.