control system capable of controlling the refrigeration capacity of a refrigeration system adapted for cooling a fluid medium , the refrigeration system being of the type including a refrigerant ; an absorbent having an affinity for the refrigerant ; an evaporator for bringing the refrigerant into heat transfer relationship with the fluid medium , the evaporator having an inlet for receiving the fluid medium to be cooled in an outlet for discharging cooled fluid medium ; an absorber in communication with the evaporator for removing refrigerant vapor therefrom ; means for supplying a concentrated absorbent - refrigerant solution to the absorber ; means for cooling the absorber to maintain the pressure therein below the pressure in the evaporator whereby refrigerant vapor migrates to the absorber to combine with the concentrated solution to produce a dilute solution ; a concentrator for removing a portion of the refrigerant from the dilute solution for recirculation to the evaporator and for providing the concentrated solution ; means for supplying the dilute solution to the concentrator ; and means for controlling the concentration of the concentrated solution supplied to the absorber for controlling the refrigeration capacity of the refrigeration system . control system includes means disposed for sensing the variations in temperature at the evaporator inlet and outlet and within the absorber for providing first , second and third tracking signal outputs indicative of the sensed temperature variations , the first tracking signal output being indicative of the variations in temperature of the fluid at the evaporator inlet , the second tracking signal output being indicative of the variations in temperature of the fluid at the evaporator outlet and the third tracking signal output being indicative of the variations in temperature in the absorber .