A COOLING DEVICE AND ITS CONTROL METHOD [001] This invention is related to a cooling device and control method wherein the yield is increased by avoiding unnecessary defrosts when the door is closed. [002] Since evaporator in cooling systems has the coolest surface inside the compartment that it is located in, moist air in the environment causes frost on the surface of evaporator. Frost accumulated on the surface of evaporator needs to be melted pe¬ riodically by the defrosting process. The period of defrosting process is determined by defrost control algorithms that are based on parameters such as the amount of frost on the evaporator, opening and closing frequency of the refrigerator's door or energy consumption; or defrosting takes place within predetermined constant time frames. Cooling efficiency is increased by avoiding frost with the defrosting process; however, since the operation requires high energy consumption, the increased energy consumption costs affect consumers. Therefore, the optimisation of the number of defrost processes and their timings provides decreased energy consumption. [003] Amount of frost accumulated on the evaporator is directly proportional to moisture level in the air that is circulating inside the cooling system. When the moisture level is high, frost accumulated increases. If the refrigerator's door stays open for a long time, since no air goes inside the refrigerator from outside, moisture level circulating in the air constantly decreases. In this case, frost accumulation on the evaporator takes a longer period. In order to decrease the energy consumption when the door is kept close for long periods, various defrost methods are developed. [004] In the United States Patent no. US4297852, when the door of the refrigerator is not opened frequently, a secondary defrost method is initiated wherein the defrost decision is made according to the proportion of the period that the door is kept open to the period that the door is kept closed. [005] In the European Patent Application no. EP1070925, when the door of the re¬ frigerator is kept closed for long periods, a secondary defrost method is initiated wherein the defrost decision is made based on the difference between the temperatures of the evaporator and the inner volume of the refrigerator. [006] The aim of this invention is to realize a cooling system and its control method where the defrost times are arranged so as to decrease the energy consumption cost of the user. [007] The cooling device and its control method designed to fulfil this aim is illustrated on the attached figures, where: [008] Figure 1 is a schematic representation of a cooling device, [009] Figure 2 is a flow chart of a cooling device control method, [010] Figure 3 and 4 is a flow chart of alternative applications of a cooling device control method. [011] Components illustrated on the drawings are numbered individually and listed below. [012] 1- Cooling device [013] 2- Freshfood compartment [014] 3- Freezing compartment [015] 4- Door [016] 5- Compressor [017] 6- Evaporator [018] 7- Defrost unit [019] 8- Thermometer [020] 9- Control card [021] 10- Memory [022] 11- Door switch [023] Cooling device (1), preferably a no-frost refrigerator, comprises a freshfood compartment (2) in which food and beverages are stored, a freezing compartment (3) in which foods are stored by being frozen, one or more doors (4) that enable access to the compartments (2 and 3), a compressor (5) that aids the execution of the cooling cycle, an evaporator (6) that provides cooling of the inner volume of the cooling device (1) by absorbing thermal energy, a defrost unit (7) that provides cleaning of frost ac¬ cumulated on the evaporator (6), a thermometer (8) that enables measurement of the temperature inside the freshfood compartment (6), one or more door switches (11) that become open when the door is open and that go off when the door is closed, a control card (9) that determines the operation periods of defrost unit (7) based on constant or variable defrost algorithms, and that delays the operation period of defrost unit (7) until the temperature of the freshfood compartment (2) exceeds a predetermined limit temperature value in a predetermined latency time, if the door (4) is not opened after the last defrost process , and a memory (10) that stores information such as defrost algorithm, next defrost time etc. [024] Control card (9) tracks the status of the door (4) that covers any of the com¬ partments (2 and 3) via the position of door switch (11) after any defrost process executed by the defrost unit (7). Succeeding defrost time that is determined by the defrost algorithm is stored in the memory (10). If the door (4) is opened before the succeeding defrost time, in other words when the door switch (11) is turned on, defrost process is executed at the predetermined time. If the door (4) is kept close, in other words door switch (11) always remains off, defrost process is delayed by the control card (9). Information gathered from the thermometer (8) is controlled continuously; defrost process does not take place if the temperature of the freshfood compartment (2) does not exceed the limit temperature value. If the temperature of the freshfood compartment (2) exceeds the limit value and remains above this limit value for a certain period, control card (9) initiates the defrost unit (7) and defrost process is performed. The longer period of the temperature of the freshfood compartment (2) exceeding the limit temperature value is an indication of the increasing amount of frost on the evaporator (6) and reveals the need for defrost process. [025] For the description of the cooling device (1) control method subject to the present invention, following symbols are used: [026] zd: Succeeding defrost time [027] Tl : Temperature of the freshfood compartment (2) [028] Ts: Limit temperature value of the freshfood compartment (2) [029] zl : Time span in which the temperature of the freshfood compartment stays above the limit temperature value (Ts) of the freshfood compartment (2) [030] zs : Limit warming period of the freshfood compartment (2) [031] z2: Defrost additional delay time [032] z3: Minimum time span between two defrost process when the door (4) is closed [033] Limit temperature value (Ts) of the freshfood compartment (2), limit warming period (zs) of the freshfood compartment (2), defrost additional delay time (z2) and minimum time span (z3) between two defrost processes when the door (4) is closed are predetermined by the manufacturer and recorded on the memory (10). [034] Defrost process of the cooling device (1) is controlled as follows: - Succeeding defrost time (zd) is computed following the completion of the defrost process (101), - It is controlled whether the door (4) is opened (102), - Waited until the succeeding defrost time (zd), if the door is opened (103), - Defrost process is performed by operating the defrost unit (7) (106), - Returned to the step where the succeeding defrost time is computed (101), - If the door (4) is not opened, temperature of the freshfood compartment (Tl) determined by the thermometer (8) is compared (104) with the limit temperature value (Ts) of the freshfood compartment (2) , - Returned to the step (102) where it is controlled whether the door is closed or not if the temperature of the freshfood compartment (Tl) is lower than the limit temperature value of the freshfood compartment (2) (Ts), - If the temperature of the freshfood compartment (Tl) is higher than the limit temperature value of the freshfood compartment (2) (Ts), time span (zl) in which the temperature of the freshfood compartment stays above the limit temperature value (Ts) of the freshfood compartment (2) is compared with the limit warming period (zs) of the freshfood compartment (2) (105), - If the time span (zl) in which the temperature of freshfood compartment stays above the limit temperature value (Ts) of freshfood compartment (2) is lower than the limit warming period (zs) of freshfood compartment (2), it is returned to the step (102), where it is controlled whether the door is closed or not, - If the time span (zl) in which the temperature of the freshfood compartment stays above the limit temperature value (Ts) of the freshfood compartment (2) is higher than the limit warming period (zs) of freshfood compartment (2), defrost is performed by operating the defrost unit (7) (106), - Returned to the step (101) where the succeeding defrost time is computed (Figure 2). [035] In another embodiment of the invention, in order to avoid a cycle where continuous defrosting could occur, the minimum time span (z3) required to take place between successive defrost processes when the doors (4) are closed, is determined. When the door (4) is in its closed position, the switch (11) is pressed but still a slight opening exists or in case hot food is loaded in the cooling device (1) or cooling is insufficient due to a failure (gas leakage etc.), since the temperature of the freshfood compartment (Tl) would always remain above the limit temperature value (Ts) of the freshfood compartment (2), a continuous cycle of defrosting would be encountered. In order to avoid that, in addition to the above mentioned steps, after the step of comparing the time span (zl) in which the temperature of freshfood compartment (2) stays above the limit temperature value (Ts) of freshfood compartment (2) to the limit warming time (zs) of freshfood compartment (2) (105), the following steps are performed: - If the time span (zl) in which the temperature of freshfood compartment (2) stays above the limit temperature value (Ts) of freshfood compartment (2) is higher than limit warming time (zs) of the freshfood compartment (2), it is checked whether the minimum time span (z3) between two successive defrost processes when the door (4) is closed, is passed or not (201), - Returned to the step (102) where it is controlled whether the door is closed or not if the minimum time span (z3) between two defrost processes when the door (4) is closed is not completed, , - If the minimum time span (z3) between two defrost process when the door (4) is closed is completed, defrost is performed by operating the defrost unit (7) (106) (Figure 3). [036] In another embodiment of the invention, after the step where it is controlled whether the door is opened or not (102), if the door (4) is found to have been opened - Whether succeeding defrost time (zd) is reached or not is checked (301), If the succeeding defrost time (zd) is not reached, the process is delayed until the next defrost time (zd) (103), - If the next defrost time (zd) is reached, the process is delayed for additional defrost delay time (z2) (302), - Defrost is performed by operating the defrost unit (7) (106) (Figure 4). For cooling devices (1), since no moisture level increase would occur as long as the door (4) is kept closed, frost accumulation on the evaporator (6) and the need for a defrost occur in a time interval longer than the normal operation conditions. When the doors (4) are closed, the defrost process is performed by taking into consideration the temperature of the freshfood compartment (Tl), which leads to less defrost processes and a decrease in energy consumption cost of the user.