A refrigerant supercooling circuit comprising a receiver (5) for retention of a liquid-phase refrigerant installed in a refrigerant line (23) connecting a first expansion valve (45) and a plurality of second expansion valves (71), an extraction line (61) for taking out the liquid-phase refrigerant in the receiver (5), a third expansion valve (62) in the extraction line, the portion of the extraction line (61) downstream of the third expansion valve (62) being passed through the receiver (5) or through a supercooling tank (63), the arrangement being such that the degree of opening of the first expansion valve (45) is controlled either according to the refrigerant pressure (P1) on a refrigerant line (20) connecting the delivery side of a compressor (2) and a four-way valve (3), or according to the degree of supercooling (SC) in the outlet of an outdoor heat exchanger (4), or according to the pressure difference across the first expansion valve (45).