Patent Publication Number: US-6701722-B1

Title: Air conditioner and method of detecting refrigerant leakage therein

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Application No. 2002-23992, filed May 1, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to air conditioners and, more particularly, to a multiunit-type air conditioner having a plurality of indoor units and used for heating or cooling indoor air, and to a method of detecting a refrigerant leakage in the air conditioner. 
     2. Description of the Related Art 
     Air conditioners are machines that control the indoor temperatures by transferring heat between refrigerant and indoor/outdoor air. FIG. 1 is a schematic view showing a construction and refrigerant flow of a conventional air conditioner, in which arrows show a refrigerant flowing direction during a cooling mode operation of the air conditioner. As shown in FIG. 1, the conventional air conditioner comprises an indoor unit  102  and an outdoor unit  104 , with an indoor heat exchanger  116  installed in the indoor unit  102 . The indoor heat exchanger  116  is a device at which heat is transferred between the refrigerant and indoor air. The indoor unit  102  also has an indoor expansion valve  114  which regulates pressure of the refrigerant flowing to the indoor heat exchanger  116  during a cooling mode operation. Two or more indoor units  102  each having the above-mentioned construction may be arranged in parallel as desired to form a multiunit-type air conditioner. 
     The outdoor unit  104  comprises an outdoor heat exchanger  122  and a compressor  118 . The outdoor heat exchanger  122  is a device at which heat is transferred between the refrigerant and outdoor air. The compressor  118  sucks low temperature and low pressure refrigerant, and compresses the low temperature and low pressure refrigerant to make high temperature and high pressure refrigerant prior to discharging the refrigerant from the compressor  118 . The outdoor unit  104  also has an outdoor expansion valve  128  which regulates pressure of the refrigerant flowing to the outdoor heat exchanger  122  during a heating mode operation. A four-way valve  130  is mounted on a refrigerant circulating line in the outdoor unit  104 , and controls a flowing direction of an output refrigerant from the compressor  118  such that the output refrigerant flows to the outdoor heat exchanger  122  or the indoor heat exchanger  116  in accordance with a selected mode of the air conditioner. 
     Extending between the indoor unit  102  and the outdoor unit  104  of the air conditioner is the refrigerant circulating line (refrigerant pipe) which guides the flow of the refrigerant between the indoor unit  102  and the outdoor unit  104 . Particularly in the case of a multiunit-type air conditioner having a plurality of indoor units  102 , the refrigerant pipe is very long in length and somewhat complex in construction, and so by integrating a plurality of short pipes having an easily-handled length to each other to form a long and complex refrigerant pipe through, for example, a welding process is necessary. However, when the welding process is not effectively or sufficiently performed at welded junctions of the refrigerant pipe or when the refrigerant pipe is not properly managed after an installation of the pipe in the air conditioner, the refrigerant pipe may be broken at the welded junctions and undesirably allow a refrigerant leakage through the broken junctions. Further, repeated operation of the air conditioner over a lengthy period of time causes the refrigerant pipe to gradually become fatigued, and, in such a case, the refrigerant pipe may be loosened at connected junctions of the refrigerated pipe, thus allowing a refrigerant leakage through the loosened junctions. When the refrigerant leakage from the refrigerant pipe occurs, the air conditioner cannot perform an operation of the air conditioner. Therefore, in such a case, a user of the air conditioner must find positions of broken or loosened junctions of the refrigerant pipe to quickly repair the refrigerant pipe and restore a desired operation of the air conditioner. 
     The refrigerant leakage from the refrigerant pipe of an air conditioner has been detected by checking a variation in pressure of the output refrigerant from the compressor. However, this method only informs a user of an occurrence of the refrigerant leakage from the refrigerant pipe, but does not allow the user to find exact positions of the broken or loosened areas of the refrigerant pipe, and so the user cannot easily or quickly repair the broken or loosened refrigerant pipe. In the case of a multiunit-type air conditioner having a very long and complex refrigerant pipe, to find the exact positions of the broken or loosened areas of the refrigerant pipe is more important than to detect an occurrence of the refrigerant leakage from the refrigerant pipe. However, to find the exact positions of broken or loosened areas of the long and complex refrigerant pipe is very difficult. Particularly, in the case of a building with a centralized air conditioning system, the refrigerant pipe of an air conditioning system is typically installed in the building at the same time as constructing the building such that the refrigerant pipe is hidden in walls, ceilings and floors. Therefore, to find the exact positions of the broken or loosened areas of the pipe in the case of a refrigerant leakage is even more difficult. 
     SUMMARY OF THE INVENTION 
     Accordingly, an air conditioner and a method of detecting a refrigerant leakage in the air conditioner are provided, in which an entire refrigerant pipe of the air conditioner is sectioned based on expansion valves into a plurality of sections, and the sections are checked one by one to quickly detect a refrigerant leakage from the sections, as well as to find an exact position of a broken or loosened area of the refrigerant pipe causing the refrigerant leakage. 
     Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In order to accomplish the above and other aspects, the present invention provides an air conditioner, comprising a compressor, an expansion valve, an outdoor heat exchanger, and an indoor heat exchanger connected to each other by a refrigerant pipe, wherein the refrigerant pipe is sectioned into a high pressure section extending from an outlet port of the compressor to an inlet port of the expansion valve, and a low pressure section extending from an outlet port of the expansion valve to an inlet port of the compressor. In the air conditioner, the control unit detects a refrigerant leakage in the low pressure section by comparing a variation in refrigerant pressure, sensed by a pressure sensor provided on the refrigerant pipe within the low pressure section, with a preset variation in the refrigerant pressure in the case of a normal operation without having a refrigerant leakage, during a refrigerant leakage detection mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and advantages of the invention will be come apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a block diagram, showing a construction of a conventional, air conditioner; 
     FIG. 2A is a block diagram, showing a construction of an air conditioner in accordance with an embodiment of the present invention; 
     FIG. 2B is a block diagram, showing a concept of refrigerant leakage detection in the air conditioner of FIG. 2A; 
     FIG. 3A is a diagrammatic view showing a pressure characteristic of a high pressure section of a refrigerant pipe included in the air conditioner of this invention; 
     FIG. 3B is a diagrammatic view showing the pressure characteristic of a low pressure section of the refrigerant pipe of FIG. 2A; 
     FIG. 4 is a flowchart of a method of detecting a refrigerant leakage in the air conditioner of FIG. 2A; 
     FIG. 5 is a block diagram, showing a refrigerant pressure distribution in the air conditioner of FIG. 2A during a cooling mode operation; 
     FIG. 6 is a block diagram, showing a refrigerant pressure distribution in the air conditioner of FIG. 2A during a heating mode operation; 
     FIG. 7 is a block diagram, showing a first detecting section in the air conditioner of FIG. 2A; 
     FIG. 8 is a flowchart of the process of detecting a refrigerant leakage in the first detecting section of FIG. 7; 
     FIG. 9 is a block diagram, showing a second detecting section in the air conditioner of FIG. 2A; 
     FIG. 10 is a flowchart of the process of detecting a refrigerant leakage in the second detecting section of FIG. 9; 
     FIG. 11 is a block diagram, showing a third detecting section in the air conditioner of FIG. 2A; and 
     FIG. 12 is a flowchart of the process of detecting a refrigerant leakage in the third detecting section of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 2A is a block diagram, showing the construction of the air conditioner in accordance with an embodiment of this invention, in which the arrows show a refrigerant flowing direction during a cooling mode operation of the air conditioner. 
     As shown in FIG. 2A, the air conditioner comprises an indoor unit  202  and an outdoor unit  204 , with an indoor heat exchanger  216  installed in the indoor unit  202 . The indoor heat exchanger  216  is a device at which heat is transferred between refrigerant and indoor air. The indoor unit  202  also has an indoor expansion valve  214  which regulates pressure of the refrigerant flowing to the indoor heat exchanger  216  during a cooling mode operation. The indoor expansion valve  214  is completely opened during a heating mode operation. This indoor expansion valve  214  is used to section first and third detecting sections, which are used in a refrigerant leakage detection mode, as will be described in detail later herein. Two or more indoor units  202  each having the above-mentioned construction may be arranged in parallel as desired to form a multiunit-type air conditioner. 
     The outdoor unit  204  comprises an outdoor heat exchanger  222  and a compressor  218 . The outdoor heat exchanger  222  is a device at which heat is transferred between the refrigerant and outdoor air. The compressor  218  sucks low temperature and low pressure refrigerant, and compresses the low temperature and low pressure refrigerant to make high temperature and high pressure refrigerant prior to discharging the refrigerant. The outdoor unit  204  has an outdoor expansion valve  228  which regulates pressure of the refrigerant flowing to the outdoor heat exchanger  222  during a heating mode operation. The outdoor expansion valve  228  is completely opened during a cooling mode operation. The outdoor expansion valve  228  is used to section a second detecting section, which is used in the refrigerant leakage detection mode, as will be described in detail later herein. 
     During a normal mode operation of the air conditioner, an opening ratio of each of the two expansion valves  214  and  228  is appropriately controlled to produce the refrigerant pressure required by the indoor units  202 . Further, the two expansion valves  214  and  228  are completely opened or closed during a refrigerant leakage detection mode, thus sectioning the refrigerant pipe into the first, second and third detecting sections. In the air conditioner, the electronic expansion valves may be used as the indoor and outdoor expansion valves  214  and  228 , since the electronic expansion valves  214  and  228  can be electronically controlled and allow a process of the refrigerant leakage detection to be automatically carried out. 
     A four-way valve  230  is mounted on the refrigerant pipe in the outdoor unit  204 , and controls a flowing direction of output refrigerant from the compressor  218  such that the output refrigerant flows to the outdoor heat exchanger  222  or the indoor heat exchanger  216  in accordance with a selected mode of the air conditioner. An input pressure sensor  236  and an input temperature sensor  238 , which are used for the refrigerant leakage detection, are sequentially mounted on the refrigerant pipe between the four-way valve  230  and the inlet port of the compressor  218 , and sense the pressure and temperature of input refrigerant flowing to the compressor  218 . In the air conditioner, data, representing the pressure and temperature of input refrigerant of the compressor  218  sensed by the two sensors  236  and  238 , is used to optimally control an operation of the air conditioner, as well as for the refrigerant leakage detection. 
     An output pressure sensor  232  and an output temperature sensor  234 , which are used for the refrigerant leakage detection, are sequentially mounted on the refrigerant pipe between the outlet port of the compressor  218  and the four-way valve  230 . Further, an outdoor temperature sensor  248  is mounted to the outdoor heat exchanger  222 . The output pressure sensor  232  detects a variation in the refrigerant pressure in the high pressure section starting at the outlet port of the compressor  218  so as to detect the refrigerant leakage from the refrigerant pipe. The output temperature sensor  234  senses the temperature of output refrigerant discharged from the compressor  218  so as to control the temperature of the output refrigerant of the compressor  218  in accordance with a sensed outdoor temperature. Since there must be a difference, higher than a predetermined level, between the temperatures of the outdoor air and the output refrigerant in order to accomplish a desired heat exchanging effect at the outdoor heat exchanger  222 , controlling the temperature of the output refrigerant is necessary. 
     FIG. 2B is a block diagram, showing a concept of the refrigerant leakage detection process in the air conditioner of FIG.  2 A. In the air conditioner, a reference pressure variation value, which represents a reduction in the refrigerant pressure per unit time during a normal operation of the air conditioner without any refrigerant leakage, is stored in a form of data in a memory  254  such that a control unit  252  refers the stored data as reference data while detecting the refrigerant leakage. That is, the control unit  252  calculates a variation in input refrigerant pressure per unit time of the compressor  218  in response to an input signal from the output pressure sensor  236 , and compares the calculated pressure variation with the reference pressure variation value stored in the memory  254  so as to determine whether a refrigerant leakage is occurring. When the refrigerant leakage from the refrigerant pipe is determined, information of the refrigerant leakage is displayed on a display unit  256 . 
     When studying a refrigerant distribution in the refrigerant pipe of an air conditioner, a relatively higher pressure section and a relatively lower pressure section are present in the refrigerant pipe at the same time. That is, the output refrigerant discharged from the compressor  218  of the outdoor unit  204  has a relatively higher pressure, and the high pressure output refrigerant is reduced in pressure while passing through the outdoor expansion valve  228 , thus becoming low pressure refrigerant. In the air conditioner, the section with the relative higher refrigerant pressure is set to a high pressure section, while the section with the relative lower refrigerant pressure is set to a low pressure section. 
     In order to accomplish a desired heat exchanging effect at the outdoor heat exchanger  222 , a difference must be secured, higher than a predetermined level, between the temperatures of the outdoor air and the refrigerant. Since the refrigerant temperature varies in proportion to the refrigerant pressure, the refrigerant pressure is regulated such that the refrigerant pressure is in proportion to a sensed outdoor temperature. That is, the refrigerant pressure in the high pressure section must be in proportion to the outdoor temperature. 
     The relation between the refrigerant pressure in the high pressure section and the outdoor temperature will be described as follows with reference to FIG.  3 A. FIG. 3A is a diagrammatic view, showing the pressure characteristic of the high pressure section of the refrigerant pipe included in the air conditioner of FIG.  2 A. As shown in FIG. 3A, when refrigerant leaks from the refrigerant pipe within the high pressure section, a variation in the refrigerant pressure of the high pressure section is larger than a variation in the outdoor temperature. Therefore, a refrigerant leakage is recognized from the refrigerant pipe when a result of a comparison of the refrigerant pressure variation in the high pressure section with the outdoor temperature variation represents that the refrigerant pressure variation is not in proportion to the outdoor temperature variation. As shown in FIG. 3A, initially when a refrigerant leakage occurs, the refrigerant pressure in the high pressure section is quickly reduced and is not in proportion to the outdoor temperature. However, after repairing a broken part of the refrigerant pipe causing the refrigerant leakage, the refrigerant does not further leak from the pipe, and so the refrigerant pressure is restored to a normal level of the refrigerant pressure. The amount of leaked refrigerant may need to be restored after repairing the broken part of the refrigerant pipe. 
     FIG. 3B is a diagrammatic view, showing the pressure characteristic of the low pressure section of the refrigerant pipe. As shown in FIG. 3B, the high pressure refrigerant is quickly reduced in pressure while passing through the outdoor expansion valve  228 , thus defining the low pressure section after the outdoor expansion valve  228 . The reduction in the refrigerant pressure per unit time in the case of a refrigerant leakage in the low pressure section is smaller than the reduction in the refrigerant pressure per unit time in the case of a normal operation without having a refrigerant leakage. That is, when there is no refrigerant leakage in the low pressure section, refrigerant pressure is normally reduced by an action of the indoor expansion  214  valve mounted on the refrigerant pipe. However, when refrigerant leaks in the low pressure section, outside air is introduced into the refrigerant pipe through a broken part, and so refrigerant pressure is abnormally reduced. Therefore, in a method of detecting a refrigerant leakage in the air conditioner, an entire low pressure section of the refrigerant pipe is sectioned into two or more subsections, and a reduction in refrigerant pressure per unit time in each subsection of the low pressure section is detected. Thereafter, each of the detected reductions in refrigerant pressure of the subsections is compared with the reduction in refrigerant pressure per unit time in the case of a normal operation so as to determine whether a refrigerant leakage occurs in an associated subsection. 
     FIG. 4 is a flowchart of the method of detecting a refrigerant leakage in the air conditioner of FIG.  2 A. As shown in FIG. 4, when the air conditioner starts an operation at S 401 , the refrigerant pressure variation in the high pressure section is compared with the outdoor temperature variation so as to determine whether a refrigerant leakage occurs from the refrigerant pipe, thus determining whether the air conditioner is operating normally at S 402 . When at S 402  a refrigerant leakage is determined to have occurred from the refrigerant pipe, the first to third detecting sections are sequentially and separately checked at S 403 , S 404  and S 405  to determine in detail a position of a broken part causing the refrigerant leakage. That is, the first detecting section is primarily checked at step S 403 . When at S 403  a refrigerant leakage is determined to have occurred in the first section, a sign representing the refrigerant leakage is displayed on a display unit  256  at S 407 . Thereafter, at S 404 , the second detecting section is secondarily checked. When at S 404  a refrigerant leakage is determined to have occurred in the second section, a sign representing the refrigerant leakage is displayed on the display unit  256  at S 407 . The third detecting section is, thereafter, checked at S 405 . When at S 405  a refrigerant leakage is determined to have occurred in the third section, a sign representing the leakage is displayed on the display unit  256  at S 407 . After sequentially checking the three sections, the refrigerant leakage checking results are stored in a form of data in a memory at S 406 . Such storage of the refrigerant leakage checking result data in the memory is for transmission of the data to a service station to allow a service man to quickly deal with the refrigerant leakage. 
     FIG. 5 is a block diagram, showing a refrigerant pressure distribution in the air conditioner during a cooling mode operation. In FIG. 5, the section shown by the solid line is a high pressure section, while the section shown by the dot-and-dash is a low pressure section. Pressure of the output refrigerant from the compressor  218  is very high. However, when an opening ratio of the indoor expansion valve  214  is appropriately regulated, such high pressure refrigerant is reduced in pressure while passing through the indoor expansion valve  214 . Therefore, the refrigerant pipe may be divided into the high pressure section and the low pressure section based on of the indoor expansion valve  214 . The refrigerant pressure distribution shown in FIG. 5 is obtained from a cooling mode operation with both the opening ratio of the indoor expansion valve  214  appropriately regulated and the outdoor expansion valve  228  completely closed. 
     FIG. 6 is a block diagram, showing a refrigerant pressure distribution in the air conditioner during a heating mode operation. In FIG. 6, the section shown by the solid line is a high pressure section, while the section shown by the dot-and-dash line is a low pressure section. The four-way valve  230  controls the refrigerant flow path such that the high pressure output refrigerant from the compressor  218  flows to the indoor heat exchanger  216 , and controls the refrigerant flow path such that the refrigerant sequentially passing through the indoor and outdoor heat exchangers  216  and  222  returns to the compressor  218 . Therefore, the refrigerant direction of flow of the air conditioner during the heating mode operation of FIG. 6 is different from that during the cooling mode operation of FIG.  5 . The refrigerant pressure distribution shown in FIG. 6 is obtained from the heating mode operation in which both the indoor expansion valve  214  is completely opened (or appropriately opened to accomplish an appropriate opening ratio) and the opening ratio of the outdoor expansion valve  228  is appropriately regulated. Therefore, the refrigerant after passing through the outdoor expansion valve  228  is reduced in the pressure of the refrigerant. 
     As shown in FIGS. 5 and 6, the section of the refrigerant pipe between the outlet port of the compressor  218  and the four-way valve  230  is fixed to a high pressure section regardless of a selected operational mode of the air conditioner, that is, for either of the cooling mode operation or the heating mode operation. However, the remaining sections of the refrigerant pipe are changeable between high and low pressure sections in response to a flow path control of the four-way valve  230  which changes the direction of the refrigerant flow in the sections in accordance with a selected operational mode of the air conditioner. 
     FIG. 7 is a block diagram, showing the first detecting section in the air conditioner. In FIG. 7, the section of the refrigerant pipe, extending from the indoor expansion valve  214  to the inlet port of the compressor  218  while passing through the indoor heat exchanger  216  and the four-way valve  230 , is the first detecting section. In this case, the air conditioner performs a cooling mode operation. During a refrigerant leakage detection mode, the indoor expansion valve  214  is completely closed, while the outdoor expansion valve  228  is completely opened. Reductions in the pressure and temperature of refrigerant in the first detecting section are sensed using the input pressure sensor  236  and the input temperature sensor  238 , which are mounted on the refrigerant pipe extending to the inlet port of the compressor  218 . 
     FIG. 8 is a flowchart of a process of detecting a refrigerant leakage in the first detecting section. As shown in FIG. 8, when the air conditioner starts an operation of the air conditioner at S 801 , the refrigerant pressure variation in the high pressure section is compared with the indoor temperature variation so as to determine whether a refrigerant leakage from the refrigerant pipe is occurring, thus determining whether the air conditioner is operating normally at S 802 . When at S 802  a refrigerant leakage from the refrigerant pipe is determined to have occurred, the first detecting section is checked at operations S 803  to S 808  to determine whether there is a refrigerant leakage in the first detecting section. That is, to check the first detecting section, the air conditioner is operated in a cooling mode at S 803 . When the indoor expansion valve  214  of the air conditioner of FIG. 7 is completely closed at S 804 , refrigerant pressure in the first detecting section is gradually reduced due to a suction force of the compressor  218 . A reduction in the refrigerant pressure per unit time in such a case is measured at S 805 , and the measured pressure reduction is compared with the reduction in the refrigerant pressure per unit time in the case of a normal operation of the air conditioner with the indoor expansion valve  214  being completely closed, at S 806 . The pressure reduction of the first detecting section per unit time measured during a refrigerant leakage detection mode is set to P 1 , and the pressure reduction of the first detecting section per unit time measured during a normal operation without a refrigerant leakage is set to Pa. In the case of P 1 &lt;Pa, a refrigerant leakage in the first detecting section is determined to have occurred. When a refrigerant leakage in the first detecting section is determined to have occurred, a sign of the refrigerant leakage in the first section is displayed on the display unit  256  at S 807 . However, when no refrigerant leakage in the first detecting section is determined, the control unit starts a process of detecting a refrigerant leakage in the second detecting section at S 808 . 
     FIG. 9 is a block diagram, showing the second detecting section in the air conditioner. In FIG. 9, the section of the refrigerant pipe, extending from the outdoor expansion valve  228  to the inlet port of the compressor  218  while passing through the outdoor heat exchanger  222  and the four-way valve  230 , is the second detecting section. In this case, the air conditioner performs a heating mode operation. During the refrigerant leakage detection mode, the outdoor expansion valve  228  is completely closed, and reductions in the pressure and temperature of refrigerant in the second detecting section are sensed using the input pressure sensor  236  and the input temperature sensor  238 , which are mounted on the refrigerant pipe extending to the inlet port of the compressor  218 . 
     FIG. 10 is a flowchart of a process of detecting a refrigerant leakage in the second detecting section. As shown in FIG. 10, when the air conditioner starts an operation of the air conditioner at S 1001 , the refrigerant pressure variation in the high pressure section is compared with the outdoor temperature variation so as to determine whether a refrigerant leakage from the refrigerant pipe is occurring, thus determining whether the air conditioner is operating normally at S 1002 . When at S 1002  a refrigerant leakage from the refrigerant pipe is determined to have occurred, the first detecting section is checked at S 1003  to determine whether there is a refrigerant leakage in the first detecting section. When at S 1003  a refrigerant leakage in the first detecting section is determined, a sign of the refrigerant leakage in the first detecting section is displayed on the display unit  256  at S 1008 , and the second detecting section is checked at S 1004  to S 1009  to determine whether there is a refrigerant leakage in the second detecting section. Further, when no refrigerant leakage in the first detecting section is determined, a refrigerant leakage in the second detecting section is checked. In order to check the second detecting section, the air conditioner is operated in a heating mode at S 1004 . When the outdoor expansion valve  228  of the air conditioner is completely closed at S 1005 , the refrigerant pressure in the second detecting section is gradually reduced. A reduction P 2  in the refrigerant pressure of the second detecting section per unit time in this case is measured at S 1006 , and the measured pressure reduction P 2  is compared with a reduction Pb in the refrigerant pressure of the second detecting section per unit time in the case of a normal operation of the air conditioner with the outdoor expansion valve  228  completely closed, at S 1007 . In the case of P 2 &lt;Pb, a refrigerant leakage in the second detecting section is determined to have occurred. When a refrigerant leakage in the second detecting section is determined to have occurred, a sign of the refrigerant leakage in the second section is displayed on the display unit  256  at S 1008 . However, when no refrigerant leakage in the second detecting section is determined, the control unit starts a process of detecting a refrigerant leakage in the third detecting section at S 1009 . 
     FIG. 11 is a block diagram, showing the third detecting section in the air conditioner. In FIG. 11, the section of the refrigerant pipe, extending from the indoor expansion valve  214  to the inlet port of the compressor  218  while passing through the outdoor expansion valve  228 , the outdoor heat exchanger  222  and the four-way valve  230 , is the third detecting section. In this case, the section from the outdoor expansion valve  228  to the inlet port of the compressor  218  is the second detecting section, and the second section has been checked as to whether a refrigerant leakage in the second section has occurred as described above with reference to FIG.  10 . Therefore, the third detecting section is recognized to be practically defined between the indoor expansion valve  214  and the outdoor expansion valve  228 . When a refrigerant leakage is detected in the third detecting section under a condition that the second detecting section is determined to be normal and does not have a refrigerant leakage, the refrigerant leakage occurs in the section from the indoor expansion valve  214  to the outdoor expansion valve  228 . Therefore, the refrigerant leakage detecting process for the third detecting section is performed assuming that the second detecting section is operating normally without having a refrigerant leakage. In order to detect a refrigerant leakage in the third section, the air conditioner performs a heating mode operation. After starting the heating mode operation of the air conditioner, a refrigerant leakage detection mode is performed with the indoor expansion valve  214  completely closed and the outdoor expansion valve  228  completely opened. Pressure and temperature reductions of the refrigerant in the third detecting section are sensed using the input pressure sensor  236  and the input temperature sensor  238 . 
     FIG. 12 is a flowchart of the process of detecting a refrigerant leakage in the third detecting section. As shown in FIG. 12, when the air conditioner starts the operation at S 1201 , the refrigerant pressure variation in the high pressure section is compared with the outdoor temperature variation so as to determine whether a refrigerant leakage from the refrigerant pipe occurs, thus determining whether the air conditioner is operating normally at S 1202 . When at S 1202  a refrigerant leakage from the refrigerant pipe is determined to have occurred, the first and second detecting sections are checked at S 1203  to determine whether a refrigerant leakage in the first and second detecting sections occurred. When at S 1203  no refrigerant leakage in the first and second detecting sections occurred, the third detecting section is checked at operations S 1204  to S 1209  to determine whether a refrigerant leakage in the third section occurred. In order to check the third detecting section, the air conditioner is operated in a heating mode at S 1204 . The outdoor expansion valve  228  of the air conditioner of FIG. 11 is completely opened at S 1205 , and the indoor expansion valve  214  is completely closed at S 1206 . In this case, the refrigerant pressure in the third detecting section is gradually reduced. A reduction P 3  in the refrigerant pressure of the third detecting section per unit time in this case is measured at S 1207 , and the measured pressure reduction P 3  is compared with a reduction Pc in the refrigerant pressure of the third detecting section per unit time in the case of a normal operation of the air conditioner with both the outdoor expansion valve  228  completely opened and the indoor expansion valve  214  completely closed, at S 1208 . In the case of P 3 &lt;Pc, a refrigerant leakage in the third detecting section is determined to have occurred. When a refrigerant leakage in the third detecting section is determined to have occurred, a sign of the refrigerant leakage in the third section is displayed on the display unit  256  at S 1209 . 
     In the refrigerant leakage detecting method, the detecting processes for the first to third detecting sections may be sequentially performed as described above. Alternatively, the detecting processes for the three sections may be selectively performed as desired. However, the leakage detecting process for the third section is performed based on the assumption that the second section is operating normally without having a refrigerant leakage. The selective leakage detecting process for the three sections may be easily accomplished by the use of drive software provided in the control unit  252  and user interface. That is, a batch-processing routine and selective processing routines of the refrigerant leakage detecting method are provided in the drive software of the control unit. Since the batch-processing and selective processing routines of the drive software cooperate with the user interface, a user may select the batch-processing routine or the selective processing routines as desired through the user interface. 
     As described above, an air conditioner and a method of detecting a refrigerant leakage in the air conditioner is provided. In the leakage detecting method, a refrigerant leakage in the entire refrigerant pipe is primarily detected, thus determining whether a refrigerant leakage occurred. Thereafter, the first to third detecting sections of the refrigerant pipe are checked through a batch-processing routine or selective processing routines to quickly determine whether a refrigerant leakage occurs in the first to third sections, as well as quickly finding the exact position of a broken or loosened area of the refrigerant pipe in the case of a refrigerant leakage, thus allowing a service man to quickly repair the broken or loosened area of the refrigerant pipe. The air conditioner effectively accomplishes the refrigerant leakage detecting mechanism only by addition of pressure and temperature sensors on the refrigerant pipe of a conventional air conditioner, and thereby is advantageous in that it does not force the air conditioner to be provided with additional hardware, which is expensive and complicates construction and production processes of the air conditioner. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.