liquid high pressure refrigerant over the line 304 the expansion valve 330 d is further connected by a line 332 d to a submerged evaporator 324 d a line 320 d is connecting sensor 306 308 d to the suction line 326 connected to the suction side of the compressor 328 the sensor 306 308 d is connected to a control unit 310 d which controls the expansion valve 330 d in this way it is possible to close or reduce the flow through the expansion valve when droplets of liquid refrigerant are measured by the sensor 306 308 d in this way it can be ensured that the suction line towards the compressor only carries dry gas and the evaporator is completely filled with liquid refrigerant a system as shown in fig5 could be used for different types of refrigerant where one possible refrigerant can be ammonia nh3 fig6 shows a coordinate system which vertical axes indicate the density of the refrigerant flowing through a sensor and the horizontal axis shows the signal level that can be indicated the curve that is shown indicates that a relatively low signal level is achieved if superheated refrigerant is passing the sensor but as the refrigerant starts to be saturated there is a rapid increase in the signal level that increase in signal level continues until the refrigerant phase becomes totally liquid indicated at fig6 is the control p band where the refrigeration system mostly is operating where there is the area around the superheated and the saturated phase operating in the said p band it is possible to avoid liquid refrigerant in the suction line towards the compressor and in that way totally avoid compressor hamming a further effect that is achieved is that the cooling system can operate very.