KR100400180B1 - Method of Controlling Temperature Automatically in the Showcase - Google Patents

Abstract

The present invention relates to a method for automatically adjusting the internal temperature of a showcase in a showcase to maintain a showcase high temperature and a defrost temperature at the time of defrosting at an appropriate temperature.

The method includes setting an initial value of a setting item stored in a memory, resetting and storing the initial value; Sensing a high temperature in the power-on to drive compressors installed at both sides of the showcase and simultaneously rotating the fan to perform a cooling operation; Checking whether a cooling operation time of the setting item has elapsed and checking whether a previous defrosting operation has been performed and a type of defrosting operation performed; Performing defrosting by compressor stop, heater and drain driving, and fan reverse rotation corresponding to one side of the showcase that has not previously performed defrosting according to the check result; And checking an error occurrence at predetermined time intervals during the operation, and displaying an error code when an error occurs.

Description

How to automatically adjust the temperature inside the showcase {Method of Controlling Temperature Automatically in the Showcase}

The present invention relates to a method for automatically adjusting the internal temperature in a showcase, and more particularly, to a method for automatically adjusting the internal temperature in a showcase to maintain a proper temperature in a showcase high temperature and a defrosting temperature during defrosting.

In general, as shown in FIG. 1, the temperature control device of the showcase installed in the supermarket and the department store includes a timer 11 for operation and defrost, a temperature sensor 12 for interior operation, a switching controller 13, and a heater ( 14, the compressor 15, the inner layer air blowing fan 16, and the outer layer air blowing fan 17 are provided.

When the power is turned on, the switching control unit 13 drives the operation and defrosting timer 11 and simultaneously supplies power to the compressor 15, the inner layer air blowing fan 16, and the outer layer air blowing fan ( 17), the compressor 15, the inner layer air blowing fan 16 and the outer layer air blowing fan 17 are driven to start the cooling operation during the set operating time, and also measured by the internal temperature sensor 12 When the temperature inside the refrigerator drops below the reference value, only the driving of the compressor 15 is stopped to maintain the cooling action. Then, when the set operating time has elapsed, the switching controller 13 turns on the heater 14 to drive the heater 14 for a set defrosting time to perform a heat generation operation to perform a defrosting operation.

As described above, the conventional temperature control device of the showcase repeatedly performs cooling and defrosting operations according to the time set in the timer, and thus relies on only the corresponding timer to control the temperature inside the refrigerator, which may cause a big problem when the timer fails. The internal temperature of the high temperature is rapidly dropped due to the heating of the heater, so it is difficult to continuously maintain the proper temperature only with the corresponding timer. In addition, since it is difficult to confirm when an error occurs in each component and only a fatal problem such as an interruption of the showcase occurs, it is difficult to operate the showcase. In addition, since all the building blocks must be operated continuously to repeat cooling and defrosting operations, there is a problem of intensifying power consumption.

In order to solve the disadvantages or problems as described above, the present invention performs the cooling and defrosting operation according to the set time, automatically alternately with two heaters installed on both sides of the showcase in accordance with the high temperature and the defrosting temperature during the cooling operation. By performing the defrosting operation, it is possible to prevent a rapid rise in the internal temperature of the refrigerator due to the heating of the heater during the defrosting and to keep it at an appropriate temperature.

In addition, the present invention tests each component block of the showcase at predetermined time intervals to check whether an error occurs and display the corresponding error when an error occurs, thereby preventing a fatal problem of stopping operation and easily healing the error. The purpose is to make it suitable for the convenience of use and continuous operation.

In addition, the present invention by using a single blow fan to rotate in the forward direction during cooling and reverse rotation during defrosting, to maintain a proper internal temperature for a long time and thereby to reduce power waste, the purpose is have.

1 is a configuration block diagram schematically showing a temperature control device of a typical showcase.

Figure 2 is a block diagram showing a system for automatically adjusting the internal temperature in the showcase according to an embodiment of the present invention.

3 is a flow chart showing a method for automatically adjusting the internal temperature in the showcase according to an embodiment of the present invention.

4 is a flowchart illustrating a process of performing a first defrost mode in FIG. 3.

FIG. 5 is a flowchart illustrating a process of performing a second defrost mode in FIG. 3.

Explanation of symbols on the main parts of the drawings

10: control unit 20: memory unit

30: switch input unit 40: load output unit

50: sensor input unit 60: temperature and setting display unit

The present invention for achieving the object as described above is to set the initial value of the setting item stored in the memory, the process of resetting and storing the initial value; Sensing a high temperature in the power-on to drive compressors installed at both sides of the showcase and simultaneously rotating the fan to perform a cooling operation; Checking whether a cooling operation time of the setting item has elapsed and checking whether a previous defrosting operation has been performed and a type of defrosting operation performed; Performing defrosting by compressor stop, heater and drain driving, and fan reverse rotation corresponding to one side of the showcase that has not previously performed defrosting according to the check result; And checking an error occurrence at predetermined time intervals during the operation, and displaying an error code when an error occurs. Preferably, the present invention stores the operation mode and the operating time currently in operation by a predetermined time unit, and applies the stored operation mode and the operating time when the system is turned off and restarted within a predetermined time due to a system error. Giving process; The method further includes the step of displaying only the selected test item or all test items in a certain order when the test request is detected, and driving a device corresponding to the test item for a predetermined time to test whether an error occurs. Characterized in that made. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the showcase according to the exemplary embodiment of the present invention, the automatic temperature control system for the inside of the refrigerator may include the control unit 10, the memory unit 20, the switch input unit 30, the load output unit 40, and the like. And a sensor input unit 50 and a temperature and setting display unit 60.

The control unit 10 controls the overall operation for automatically adjusting the internal temperature of the showcase by controlling the operation of each component block.

The memory unit 20 stores control programs and related data necessary for the control unit 10. In addition, the memory unit 20 stores a plurality of setting items for performing the automatic internal temperature adjustment operation of the showcase and initial values of the respective setting items, and the setting items are provided for setting the operation time of the compressor. A defrost interval setting item, a defrost time setting item, an item for setting a proper internal temperature, an item for setting a hysteresis of an internal temperature to maintain an appropriate internal temperature, an item for setting an appropriate heater temperature, An item for setting the hysteresis of the heater temperature to maintain the proper heater temperature, an item for displaying the version (Version) for the control program of the control unit 10 and an item for resetting all the reset values to the initial value Is done. Here, the hysteresis of the high temperature means the deviation between the set high temperature for driving the compressor to maintain the cooling temperature in the high temperature and the set high temperature off temperature for stopping the operation of the compressor, the hysteresis of the heater temperature is the defrost in the It means a deviation between the set heater on temperature for driving the heater and the set heater off temperature for stopping the driving of the heater to maintain the temperature.

The switch input unit 30 includes an item switch 31 for selecting setting items stored in the memory unit 20, an increase switch 32 for increasing and decreasing an initial value of each setting item to a desired setting value; And a reduction switch 33 and an input switch 34 for confirming the changed set value.

The load output unit 40 drives the fan motor 41 for smoothly cooling or defrosting by rotating the fan motor in a forward or reverse direction and a first heater (Heater) installed at one side of the showcase to perform defrosting operation. The first heater driver 42 for performing, the second heater driver 43 for performing the defrost operation by driving the second heater installed on the other side of the showcase, and the first compressor installed on one side of the showcase ( A first compressor driver 44 for driving a compressor by performing a cooling operation, a second compressor driver 45 for driving a second compressor installed on the other side of the showcase, and performing a cooling operation; The drainage of the melted water during the operation of the first drain driver 46 and the second heater driver 43 to smoothly discharge the melted water to the outside during the operation of the heater driver 42 smoothly outside For outflow 2 comprises a drain driver (47).

The sensor input unit 50 may include an in-vehicle sensor 51 for measuring the in-vehicle temperature, a first defrost sensor 52 for measuring the temperature of the first heater when the first heater driver 42 is operated, and And a second defrost sensor 53 for measuring the temperature of the second heater when the two heater driver 43 operates.

The temperature and setting display unit 60 is turned off normally, and under the control of the control unit 10, the setting item and setting value at the time of data setting, the test item at the test mode, the error code when an error occurs, the current height It displays the internal temperature value at the temperature check, the defrost temperature value of the first and second heaters at the time of defrosting, the operation state of the showcase, and the like.

Referring to the flowchart of FIG. 3, the method for automatically adjusting the internal temperature of the showcase according to an exemplary embodiment of the present invention is as follows.

First, the initial value of each setting item stored in the memory unit 20 has already been set to an optimal value for smoothly performing the automatic internal temperature adjustment in the showcase after many tests by the developer of the showcase. The initial value can be reset in consideration of the installation environment and operation environment.For example, in the case of the defrosting interval setting item, the initial value can be set to 3 hours, but can be changed to 1 to 12 hours. The initial value is set to 11 minutes but can be varied from 1 to 60 minutes. The internal temperature setting item can be set to -23 ° C but can be changed to -35 to 40 ° C. The initial value can be set to ± 2 ℃ but can be changed to ± 1 ~ 5 ℃. The heater temperature setting item can be set to -5 ℃ but can be changed to -15 ~ 40 ℃. The terrestrial setting item sets the initial value to ± 1 ℃ but can vary from ± 1 to 5 ℃. The version item is displayed as 'u10' but is automatically recorded according to the control program version of the controller 10. The setting item changes the setting values of all the reset items to the initial value when the input switch 34 of the switch input unit 30 is turned on in the clear state (indicated by 'Clr'). That is, when the developer or the user of the showcase is set through the switch input unit 30 to change the initial value of each setting item stored in the memory unit 20, the control unit 10 detects the switch input unit 30. At the same time, the item to be set and the initial value are displayed and the value reset through the switch input unit 30 is re-stored in the memory unit 20 (step S1). In addition, the controller 10 may analyze the performance of each setting item during the normal operation to automatically compensate and change the reset value so that the automatic internal temperature adjustment is optimally performed.

In more detail, when the item switch 31 of the switch input unit 30 is turned on to select a setting item for which the initial value is to be changed, the control unit detects the setting item and the setting item stored in the memory unit 20 and the corresponding setting item. Read the initial value of and control the temperature and setting display unit 60 to display the read setting items and the initial value.

At this time, if the corresponding item switch 31 is turned on again to select the next setting item, the controller 10 detects this and reads and displays the next setting item and the initial value of the setting item currently being displayed. In addition, in order to change the initial value to the desired setting value, when the increase switch 32 or the decrease switch 33 of the switch input unit 30 is turned on, the control unit 10 detects this and increases the currently displayed setting value. Alternatively, the display is reduced and displayed. Then, when the input switch 34 of the switch input unit 30 is turned on, the control unit 10 detects this, determines the corresponding setting value, and stores it in the memory unit 20.

The controller 10 cancels the setting mode when there is no input of the switch input unit 30 for a predetermined time (for example, 20 minutes) in the setting mode as described above, and after selecting the initial value setting item, the input switch ( When 34) is turned on, all setting values are changed to initial values and stored in the memory unit 20.

On the other hand, when the user turns on the power of the showcase, the control unit 10 detects this (step S2) and after a predetermined time (for example, 3 seconds) has elapsed, the control program and the associated program from the EEPROM of the memory unit 20. Normal operation is performed by reading data, that is, data and operating time of an operation mode. At this time, if the on of the input switch 34 is detected during the normal operation, the current internal temperature is checked and displayed. The operation mode includes a first cooling mode for performing forward driving of the fan driver 41 and driving of the compressor drivers 44, 45, reverse driving of the fan driver 41, and driving of the first heater driver 42. A first defrost mode for stopping the first compressor driver 44 and driving the first drain driver 46, a second cooling mode for performing the same driving as the first cooling mode, and a fan driver Reverse driving of the 41, driving of the second heater driving unit 43, stopping of the second compressor driving unit 45, and driving of the second drain driving unit 47 are performed in the order of the second defrost mode. In order to prevent a sudden drop in the cooling effect due to the rise in temperature during defrosting, the operation is repeated in the order of cooling, defrosting on one side, cooling, and defrosting on the other side.

In other words, the control unit 10 controls the fan drive unit 41 to perform the first cooling mode so that the fan is rotated forward and the compressor drive units 44 and 45 are driven to drive two compressors. After the internal temperature is lowered (step S3), the timer is operated to check whether the set value of the defrost interval setting item stored in the memory unit 20, that is, the cooling operation time, has elapsed (step S4). When the cooling operation time has not elapsed in the fourth process S4, the controller 10 receives the internal temperature from the internal sensor 51 of the sensor input unit 50, and the received current internal temperature is stored in the memory unit 20. Is compared with whether or not the set value (hereinafter referred to as the off-off temperature in the high temperature) of the high-temperature setting item stored in the step S has been reached (step S5).

Accordingly, when the current internal temperature reaches the internal temperature of the internal high temperature in the fifth process S5, the compressor driving units 44 and 45 are controlled to stop the two compressors, and the fan driving unit 41 is controlled to control the fan. This reverse rotation is performed to remove the accumulated dust in the condenser so that the efficiency decrease does not occur during the cooling of the internal temperature of the next cycle, and then the fourth step S4 is performed (step S6). At this time, the time during the execution of the sixth process (S6) is not included in the cooling operation time.

After performing the sixth process (S6), if the current internal temperature and the internal off temperature does not match in the fifth process (S5), the received current internal temperature is stored in the memory unit 20 It is compared whether or not the set value of the hysteresis setting item (hereinafter referred to as high temperature inside temperature) has been reached (step S7). For example, when the set value of the high temperature set item is -23 ° C and the set value of the high temperature set temperature hysteresis setting item is ± 2 ° C, the high temperature inside temperature becomes -21 ° C.

At this time, if the present temperature in the high temperature does not reach the temperature inside the high temperature to perform the fourth process (S4) again, and if the current temperature in the high temperature reaches the high temperature inside the third process (S3) again. The fan drive unit 41 is controlled to perform the fan rotation in the forward direction, and at the same time, the compressor drive units 44 and 45 are controlled to drive the two compressors to lower the temperature in the refrigerator.

On the other hand, when the cooling operation time has elapsed in the fourth process (S4), the controller 10 checks whether the defrost mode is performed before performing the first cooling mode and which defrost mode is performed ( Process S8). In this case, if the defrost mode is not performed before the first cooling mode or the second defrost mode is performed before the first cooling mode, the controller 10 performs the first defrost mode (step S9). On the other hand, if the first defrost mode is performed, the second defrost mode is performed (step S10).

The first defrost mode operation is similar to the flowchart of FIG. 4. First, the controller 10 turns off the first compressor driver 44 to stop the first compressor, and the first heater driver 42 and the first drain driver ( 46), the first heater and the first drain are driven, and the fan drive unit 41 is controlled to rotate the fan in reverse to defrost one side of the showcase (step S9-1). At this time, the other side of the showcase keeps the second compressor driver 45 on to continue the cooling operation so that the second compressor is continuously driven, thereby preventing the internal temperature of the showcase from rapidly increasing, and also the memory. It is checked whether the set value of the defrost time setting item stored in the unit 20, that is, the defrost operation time has elapsed (step S9-2).

If the defrosting operation time has not elapsed in step 9-2 (S9-2), the controller 10 receives the first heater temperature from the first defrost sensor 52 of the sensor input unit 50 and receives the corresponding heater. It is compared whether the current first heater temperature reaches the set value of the heater temperature setting item stored in the memory unit 20, that is, the heater off temperature (step S9-3). Accordingly, when the current first heater temperature reaches the heater off temperature, the first heater driver 42 is turned off to stop the first heater, and then the above-described second step S9-2 is performed (S9-2). Process S9-4).

After the process 9-9 (S9-4), if the first heater temperature drops again due to the continuous driving of the second compressor, and the first heater temperature and the heater off temperature do not match, the received current It is compared whether the first heater temperature has reached the set value of the heater temperature hysteresis setting item stored in the memory unit 20, that is, the heater on temperature (step S9-5). For example, when the setting value of the heater temperature setting item is -5 ° C and the setting value of the heater temperature hysteresis setting item is ± 1 ° C, the heater on temperature is -6 ° C.

At this time, if the current first heater temperature does not reach the heater on temperature, the process of step 9-2 is performed again. If the current first heater temperature reaches the heater on temperature, it is again performed. By controlling the first heater driver 42 to drive the first heater to increase the temperature of the first heater by performing the ninth process (S9-1), the cooling efficiency due to the buildup is not reduced. do.

When the defrosting operation time has elapsed in step 9-2 (S9-2), the controller 10 cools the internal temperature of the showcase in the second cooling mode, and performs the same operation as the above-described first cooling mode. (Step S9-6).

The second defrost mode operation is similar to the flowchart of FIG. 5. First, the controller 10 turns off the second compressor driver 45 to stop the second compressor, and the second heater driver 43 and the second drain driver ( 47), the second heater and the second drain are driven, and the fan driving unit 41 is controlled to rotate the fan in reverse to defrost the other side of the showcase (step S10-1). At this time, one side of the showcase keeps the first compressor driving unit 44 on to continuously operate the first compressor to continuously perform the cooling operation, thereby preventing the internal temperature of the showcase from rising sharply and also defrosting operation. Check whether time has elapsed (step S10-2).

If the defrosting operation time has not elapsed in step 9-2 (S9-2), the controller 10 receives the second heater temperature from the second defrost sensor 53 of the sensor input unit 50 and receives the corresponding heater. It is compared whether the received current second heater temperature reaches the heater off temperature (step S10-3). Accordingly, when the current second heater temperature reaches the heater off temperature, the second heater driver 43 is turned off to stop the second heater, and then the second step S10-2 is performed again (step S10-2). Process S10-4).

After performing the step 10-4 (S10-4), if the second heater temperature drops again due to continuous driving of the first compressor, and the current second heater temperature and the heater off temperature does not match, the received current current 2 Compare whether the heater temperature has reached the heater on temperature (step S10-5). At this time, when the current second heater temperature does not reach the heater on temperature, the process 10-2 is performed again (S10-2). When the current second heater temperature reaches the heater on temperature, the second heater temperature is again. The second heater driver 43 is controlled by performing the 10-1 process (S10-1) so as to drive the second heater to increase the temperature of the second heater so that the cooling efficiency due to the buildup is not reduced. ..

When the defrosting operation time has elapsed in step 10-2 (S10-2), the controller 10 cools the inside temperature of the showcase in the first cooling mode described above.

Meanwhile, the controller 10 automatically stores the operation time and the current operation mode of each setting item in the EEPROM of the memory unit 20 at predetermined time units, for example, at intervals of about 15 minutes. When the system is turned off due to a system error such as off, and restarts within a predetermined time (for example, 15 minutes), the controller operates in the stored operating time and operation mode.

On the other hand, when the developer or user of the showcase requests through the switch input unit 30 for the system test, for example, when the power switch is turned on after the increase switch 32 and the decrease switch 33 are turned on, the control unit 10 ) Detects this, reads the control program and related data, that is, the data of the test mode, from the EEPROM of the memory unit 20, displays the test item, and enters the test mode. At this time, the item switch 31 and the input switch Only the test item selected through 34 is tested, or the entire test item is automatically run by the corresponding control program for a predetermined time (for example, 15 seconds) in a predetermined order to test whether an error occurs.

For example, after the fan is rotated for 15 seconds in the forward and reverse directions, respectively, the fan is stopped and the fan is rotated for 15 seconds in the order of the first heater, the second heater, the first drain, the second drain, the first compressor, and the second compressor. After each drive, the motor stops, and the fan defrosting, the first heater, and the first drain are performed for 15 minutes by the first defrost mode test, and after 15 seconds, all of them are turned off, and then the heater temperature of the first defrost sensor 52 is displayed. In the second defrost mode test, the fan reverse rotation, the second heater, and the second drain are performed for 15 minutes, and after 15 seconds, all of them are turned off, and then the heater temperature of the second defrost sensor 53 is displayed and the load The sequential test tests the load by repeating the fan forward rotation, fan reverse rotation, the first heater, the second heater, the first drain, the second drain, the first compressor, and the second compressor five times for two seconds.

The test mode is terminated after checking whether an error occurs by performing the above test, and when the test item is selected, the test mode is terminated when no switch is input for a predetermined time (for example, 20 minutes), and the test operation is performed. If there is an input of the item switch 31 before the specified test operation time during execution, the previous load test during operation is stopped and the next item is moved.

On the other hand, the controller 10 checks whether or not an error occurs through a test of the sensor input unit and a load sequential test at predetermined time intervals even during normal operation, and displays an error code when the error occurs and a large number of corresponding errors. If it is open, it displays the sequence at predetermined time intervals (for example, 1 second) .In this case, only error codes can be displayed and the normal operation can be continued unless the error is a fatal effect on normal operation. Make sure

For example, an error is displayed when the temperature inside the compressor detects a predetermined time (for example, 30 minutes) for a predetermined time (for example, 30 minutes) after the on / off of the compressor once at a temperature inside the refrigerator. When detected, the error is cleared, and the error is displayed at the short and the open of the in-vehicle sensor, the first defrosting sensor, or the second defrosting sensor.

As described above, according to the present invention, the two compressors are driven according to the internal temperature and the defrost temperature to perform cooling and defrosting by alternately performing the compressor stop and heater operation of one side during defrosting. In the case of defrosting, it is possible to prevent a rapid rise in the internal temperature due to the heating of the heater and to keep the defrosting temperature at an appropriate temperature. In addition, according to the present invention, by using one blower fan, it rotates forward when cooled, and reversely rotates when reaching an appropriate temperature and defrosting to maintain a proper internal temperature for a long time, thereby reducing power waste.

In addition, according to the present invention, each component block of the showcase is tested at predetermined time intervals to determine whether an error occurs and the corresponding error is displayed when an error occurs, thereby preventing a fatal problem of stopping operation and easily preventing an error. It is curable and is suitable for convenience of use and continuous operation.

Claims (5)

Setting an initial value of a setting item stored in a memory, and resetting and storing the initial value; Sensing a high temperature in the power-on to drive compressors installed at both sides of the showcase and simultaneously rotating the fan to perform a cooling operation; Checking whether a cooling operation time of the setting item has elapsed and checking whether a previous defrosting operation has been performed and a type of defrosting operation performed; Performing defrosting by compressor stop, heater and drain driving, and fan reverse rotation corresponding to one side of the showcase that has not previously performed defrosting according to the check result; Checking whether or not an error occurs at a predetermined time interval during the operation of the operation, automatic display temperature adjustment method in the showcase characterized in that it comprises a step of displaying an error code when the error occurs. The method of claim 1, Storing the current operation mode and operation time in predetermined time units and applying the stored operation mode and operation time when the system is turned off and restarted within a predetermined time due to a system error; When the test request is detected, the method further includes displaying only the selected test items or the entire test items in a certain order, and simultaneously driving a device corresponding to the test items for a predetermined time to test whether an error occurs. Auto temperature adjustment method in the showcase, characterized in that made. The method of claim 1, The performing of the cooling operation may include: stopping the driving of the compressors by comparing whether the current internal temperature has reached the internal off temperature of the setting item during the cooling operation time and simultaneously rotating the fan in reverse to maintain the internal temperature; Comparing the current internal temperature with the internal temperature of the setting item if the current internal temperature and the internal temperature OFF do not coincide after the internal temperature maintaining step; Checking whether the cooling operation time has elapsed when the current internal temperature does not reach the high temperature; And operating the compressors at the same time when the temperature in the high temperature reaches the high temperature, and performing a cooling operation by forwardly rotating the fan to perform the cooling operation in the showcase. The method of claim 1, The defrosting operation may be performed by stopping the first compressor, driving the first heater and the first drain, and rotating the fan in reverse direction when the defrosting mode is not performed before the cooling operation is performed or when the second defrosting mode is performed. Defrosting the side; Comparing whether a current first heater temperature reaches a heater off temperature of the setting item during a defrosting operation time of the setting item; Stopping the first heater when the current first heater temperature reaches the heater off temperature; If the current first heater temperature and the heater off temperature do not coincide after the first heater stop step, comparing the current first heater temperature with the heater on temperature of the setting item; Re-driving the first heater when the current first heater temperature reaches the heater on temperature and checking whether the defrosting operation time has elapsed when the first heater temperature does not reach the heater temperature; And operating the compressors when the defrosting operation time has elapsed and simultaneously rotating the fan to perform the cooling operation again. The method of claim 1, The defrosting operation may include defrosting the other side of the showcase by stopping the second compressor, driving the second heater and the second drain, and rotating the fan in the reverse direction when the first defrost mode is performed before the cooling operation is performed. ; Comparing whether a current second heater temperature reaches a heater off temperature of the setting item during a defrosting operation time of the setting item; Stopping the third heater when the current second heater temperature reaches the heater off temperature; Comparing the current second heater temperature to the heater on temperature of the setting item when the current second heater temperature and the heater off temperature do not coincide after the second heater stop step; Re-driving the second heater when the current second heater temperature reaches the heater on temperature, and checking whether the defrosting operation time has elapsed when the second heater temperature does not reach the heater temperature; When the defrosting operation time has elapsed, the step of driving the compressor and at the same time rotating the fan forward to perform the cooling operation further comprises the step of automatically adjusting the internal temperature in the showcase.