In the cooling system of a two-door type refrigerator with freezer (2) and fresh food compartments (1), the total running time (tquick) of the Quick Freeze is equal to the sum of the quick freeze 100% running time (t100) and the quick freeze cyclic running times (tcycle). The duration and temperature values at which the compressor (7) has to be operated for the quick freeze process and the operational period of the heater (5) placed in the fresh food compartment (1) to avoid the decrease of the inner temperature of the fresh food compartment (1) during quick freezing, as well as the temperature value at which the heater has to be operated are determined in the control unit (8).