of which is controlled by a solenoid valve 16 the solenoid valve 16 is controlled by a thermostat 17 which responds to a detector probe 18 to allow or stop the refrigerant circulating in the circuit or coil 19 of the evaporator the return of the refrigerant to the condensation unit is effected by means of pipes 20 connected to a return line 20a which leads to a heat exchanger 21 the heat exchanger 21 communicates with each of the suction pipes 22a 22b and 22c of the compressors 2 3 and 4 each compressor is fitted with a decompression valve 23 24 25 connected in parallel to the starting coil of each compressor motor 2a 3b 4c so as to directly connect the suction circuit 22 of the compressor and the delivery pipes 5 6 7 which include back pressure valves 5a 6b 7c according to another characteristic feature of the invention an automatic pressure release valve or means 26 responding to suction pressure is provided located in a bypass position between the delivery pipes 5 6 7 of the compressors and the heat exchanger 21 the suction pipes 22a 22b 22c of the compressors each have a tap 27a 27b 27c which are each connected to low pressure pressostats p 1 p 2 p 3 regulated in order of increasing pressure each pressostat is connected to a switch 29 when one of the evaporators 13 comes into operation its solenoid valve 16 opens the refrigerant liquid circuit the pressure on the suction side of the compressor 2 rises and actuates the pressostat p 1 thereby starting up the compressor 2 if this compressor is of a power.