Patent Publication Number: US-2023152015-A1

Title: Air conditioner

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application, under 35 U.S.C. § 111(a), of International Patent Application No. PCT/KR2022/010976, filed on Jul. 26, 2022, which claims the benefit of Korean Patent Application No. 10-2021-0158489, filed Nov. 17, 2021, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference as a part of this application. 
    
    
     BACKGROUND 
     Field 
     The disclosure relates to an air conditioner having an improved refrigerant pipe structure. 
     Description of Related Art 
     In general, an air conditioner, as an apparatus for providing comfortable indoor air, may control temperature, humidity, and air current distribution to be suitable for human activities of an indoor space and also eliminate dust from air. In general, the air conditioner includes a refrigeration cycle including a compressor, a condenser, an expansion device, and an evaporator, and may perform a cooling or heating operation according to a circulation direction of a refrigerant. 
     The air conditioner is generally configured such that one indoor unit is connected to one outdoor unit, hut recently, there is an increasing demand for a multi-type air conditioner in which several indoor units having various shapes and capacities are connected to one outdoor unit. 
     Such a multi-type air conditioner may be divided into a single pipe structure and a multi-pipe structure according to the shape of the refrigerant pipe. The single pipe structure is a structure in which a single main pipe is provided from an outdoor unit, and sub pipes from the single main pipe are connected to respective indoor units through a branch device. The multi-pipe structure is a structure in which each indoor unit is connected to an outdoor unit through a separate pipe. For example, a commercial indoor unit having a built-in expansion valve may be installed in a single-pipe structure, and a household indoor unit not having a built-in expansion valve may be installed in a multi-pipe structure. The single pipe structure air conditioner may be used in a commercial area, and the multi pipe structure air conditioner may be used in a residential area. 
     However, since a single-pipe structure air conditioner and a multi-pipe structure air conditioner are not compatible with each other, when an indoor unit is additionally installed or the type of an indoor unit is changed, a separate connection part may be required or the outdoor unit may need to be changed. Accordingly, the pipe connection may become long and complicated. 
     In addition, as residential areas and commercial areas are mixed in recent years, there is a need for a pipe structure in which a single-pipe structure and a multi-pipe structure are integrated. 
     SUMMARY 
     According to an aspect of the disclosure, there is provided an air conditioner including: an outdoor unit including a compressor and an outdoor heat exchanger a first indoor unit including a first indoor heat exchanger; and a second indoor unit including a second indoor heat exchanger and an indoor expansion valve, wherein the outdoor unit includes: an outdoor expansion valve; a first outdoor pipe provided with the outdoor expansion valve, the first outdoor pipe allowing a refrigerant discharged from the outdoor heat exchanger to pass through the outdoor expansion valve and flow to the first indoor unit; and a second outdoor pipe allowing a refrigerant discharged from the outdoor heat exchanger to bypass the outdoor expansion valve and flow to the second indoor unit. 
     The air conditioner may further include: a first connection pipe connecting the outdoor unit to the first indoor unit by connecting to the first outdoor pipe of the outdoor unit; and a second connection pipe connecting the outdoor unit to the second indoor unit by connecting to the second outdoor pipe of the outdoor unit. 
     The outdoor unit may further include: a first connection valve connecting the first outdoor pipe to the first connection pipe; and a second connection valve connecting the second outdoor pipe to the second connection pipe. 
     The refrigerant passing through the outdoor expansion valve may pass through the first connection valve and the first connection pipe and then flow into the first indoor heat exchanger, and the refrigerant bypassing the outdoor expansion valve may pass through the second connection valve and the second connection pipe and then flow into the indoor expansion valve. 
     The air conditioner may further comprise a plurality of first indoor units, the plurality of first indoor units including the first indoor unit; a plurality of first outdoor pipes, the plurality of first outdoor pipes including the first outdoor pipe; a plurality of first connection valves, the plurality of first connection valves including the first connection valve; and a plurality of first connection pipes, the plurality of first connection pipes including the first connection pipe; the plurality of first outdoor pipes, the plurality of first connection valves, and the plurality of first connection pipes may be respectively connected in series to form a plurality of refrigerant lines, and each of the plurality of first indoor units may correspond to a respective one of the plurality of refrigerant lines to be connected to the outdoor heat exchanger. 
     The air conditioner may further comprise a plurality of second indoor units, the plurality of second indoor units including the second indoor unit, and the second connection pipe may include: a main connection pipe provided to be connected to the second connection valve; and a plurality of sub connection pipes branched from the main connection pipe and each of the plurality of sub connection pipes corresponding to a respective one of the plurality of second indoor units. 
     The first connection valve has at least one of a shape, a form, a size, and a color different from those of the second connection valve so that the first connection valve and the second connection valve are visually identifiable from each other. 
     The outdoor unit may further include a valve marker configured to indicate a connection state of the first connection valve and the second connection valve. 
     The outdoor unit may further include an outdoor unit communicator to communicate with the first indoor unit and the second indoor unit, the outdoor unit communicator configured to receive information on whether the first indoor unit includes an indoor expansion valve and information on whether the second indoor unit includes an indoor expansion valve. 
     The air conditioner may further include a controller configured to control the valve marker based on the information received from the outdoor unit communicator. 
     The air conditioner may further include: a third connection pipe connecting the first indoor unit to the outdoor unit such that a refrigerant discharged from the first indoor unit is introduced into the outdoor unit; and a fourth connection pipe connecting the second indoor unit to the outdoor unit such that a refrigerant discharged from the second indoor unit is introduced into the outdoor unit. 
     The outdoor unit may further include: a third outdoor pipe through which the refrigerant flowing through the third connection pipe is introduced; and a fourth outdoor pipe through which the refrigerant flowing through the fourth connection pipe is introduced, wherein the third outdoor pipe and the fourth outdoor pipe may be provided to join before being introduced into the compressor. 
     The outdoor unit may further include: a third connection valve connecting the third outdoor pipe to the third connection pipe; and a fourth connection valve connecting the fourth outdoor pipe to the fourth connection pipe. 
     The third connection valve has at least one of a shape, a form, a size, and a color different from those of the fourth connection valve so that the third connection valve and the fourth connection valve may be visually identifiable from each other. 
     The air conditioner may further include a four-way valve configured to switch a flow path such that a refrigerant compressed by the compressor selectively flows to the outdoor heat exchanger or to the first indoor heat exchanger and the second indoor heat exchanger. 
     An air conditioner including: an outdoor unit including a compressor and an outdoor heat exchanger; a first indoor unit including a first indoor heat exchanger; a second indoor unit including a second indoor heat exchanger; a first pipe connecting the outdoor heat exchanger to the first indoor heat exchanger; a second pipe connecting the outdoor heat exchanger to the second indoor heat exchanger, an outdoor expansion valve provided inside the outdoor unit, the outdoor expansion valve disposed on one side of the first indoor heat exchanger on the first pipe and configured to expand a refrigerant under reduced pressure, an indoor expansion valve provided inside the second indoor unit, the indoor expansion valve disposed on one side of the second indoor heat exchanger on the second pipe and configured to expand a refrigerant under reduced pressure; a first connection valve disposed between the outdoor expansion valve and the first indoor heat exchanger to control the amount of refrigerant flowing through the first pipe; and a second connection valve disposed between the first connection valve and the outdoor heat exchanger to control the amount of refrigerant flowing through the second pipe; 
     The first connection valve and the second connection valve may be provided to be mutually identifiable from each other. 
     A portion of the refrigerant discharged from the outdoor heat exchanger may pass through the outdoor expansion valve to be supplied to the first indoor heat exchanger via, and the remaining of the refrigerant discharged from the outdoor heat exchanger may bypass the outdoor expansion valve to be supplied to the indoor expansion valve. 
     The outdoor heat exchanger may be provided to condense the refrigerant, and the first indoor heat exchanger and the second indoor heat exchanger may be provided to evaporate the refrigerant. 
     Each of the first indoor unit and the second indoor unit may be provided in plural. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating an air conditioner according to an embodiment. 
         FIG.  2    is a schematic diagram illustrating an air conditioner according to an embodiment. 
         FIG.  3    is a schematic diagram illustrating an air conditioner according to an embodiment. 
         FIG.  4    is a schematic diagram illustrating an air conditioner according to an embodiment. 
         FIG.  5    is a diagram schematically illustrating a cooling operation mode of the air conditioner shown in  FIG.  1   . 
         FIG.  6    is a diagram schematically illustrating a heating operation mode of the air conditioner shown in  FIG.  1   . 
         FIG.  7    is a control block diagram illustrating an air conditioner according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described in the specification and configurations shown in the accompanying drawings are merely examples of the present disclosure, and various modifications may replace the embodiments and the drawings of the present disclosure. 
     Further, identical symbols or numbers in the drawings of the present disclosure denote components or elements configured to perform substantially identical functions. 
     Further, terms used herein are only for the purpose of describing particular embodiments and are not intended to limit to the present disclosure. The singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It need to be further understood that the terms “include,” “including,” “have,” and/or “having” specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     When a part is referred to as being “connected to” another part, it may not only be directly connected to the other part but may also be indirectly connected to the other part. Similarly, when a part is referred to as being “coupled to” another part, it may not only be directly coupled to the other part but may also be indirectly coupled to the other part. Similarly, 
     In the description of an embodiment, it will be understood that, when a layer is referred to as being “on/under” another layer or substrate, it may be directly on/under the other layer or substrate, or one or more intervening layers may also be present. 
     Further, it need to be understood that, although the terms “first,” “second,” etc. may be used herein to describe various elements, the elements are not limited by the terms, and the terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element without departing from the scope of the present disclosure. The term “and/or” includes combinations of one or all of a plurality of associated listed items. 
     Hereinafter, an embodiment according to the disclosure will be described in detail with reference to the accompanying drawings. 
     An air conditioner  1  may include an outdoor unit  10  and at least one indoor unit  20  and  30 , The air conditioner  1  may include an outdoor unit  10 , a first indoor unit  20  not including an indoor expansion valve, and a second indoor unit  30  including an indoor expansion valve  38 . In the drawings, the outdoor unit  10  is illustrated as one outdoor unit, but the outdoor unit  10  may be provided as a plurality of outdoor units to which at least one indoor unit  20  and  30  is connected. 
     Hereinafter, embodiments according to the disclosure will be described with reference to  FIGS.  1  to  4   . For the sake of convenience of description, the description of  FIGS.  1  to  4    will be made in relation to a cooling operation mode of the air conditioner  1  unless otherwise stated. 
     Referring to  FIG.  1   , the air conditioner  1  may include the outdoor unit  10 , the first indoor unit  20 , and the second indoor unit  30 . In  FIG.  1   , the first indoor unit  20  and the second indoor unit  30  are each illustrated as one indoor unit, but the disclosure is not limited thereto. At least one first indoor unit  20  may be provided. At least one second indoor unit  30  may be provided. 
     The air conditioner  1  may include a connection pipe  40  connecting the outdoor unit  10  to the indoor units  20  and  30 . 
     The outdoor unit  10  may include a compressor  15 , an outdoor heat exchanger  11 , a fan motor  12 , an outdoor fan  13 , and a refrigerant pipe P 1 . 
     The compressor  15  may compress a refrigerant. For example, the compressor  15  may compress a refrigerant in a low-temperature and low-pressure gas state sucked through a suction side  15   a  and discharge a refrigerant in a high-temperature and high-pressure gas state through a discharge side  15   b.    
     The outdoor heat exchanger  11  may be provided outdoors to perform heat exchange between outdoor air and a refrigerant. The outdoor heat exchanger  11  is provided as a condenser for condensing a refrigerant in a cooling operation mode, and as an evaporator for evaporating a refrigerant in a heating operation mode. 
     The outdoor fan  13  may forcibly blow the outdoor air so that heat exchange between the outdoor air and the refrigerant is performed in the outdoor heat exchanger  11 . The outdoor fan  13  may be driven by the fan motor  12 . 
     The outdoor unit  10  may include an accumulator  14 . The accumulator  14  may be provided on the suction side  15   a  of the compressor  15  to separate the refrigerant into a liquid and a gas. The accumulator  14  may convert the refrigerant sucked into the compressor  15  into a gas in a perfect gaseous state. 
     A four-way valve  16  may switch a flow path so that the refrigerant compressed by the compressor  15  flows to the outdoor heat exchanger  11  or indoor heat exchangers  21  and  31 . The four-way valve  16  may be switched to change the flow of a refrigerant according to an operation mode (a cooling operation mode or a heating operation mode) selected by the user. 
     The four-way valve  16  may include a first port  161 , a second port  162 , a third port  163 , and a fourth port  164 . 
     The first port  161  may be connected to the compressor  15 . The first port  161  may be connected to the suction side  15   a  of the compressor  15  through a refrigerant pipe  186 . The second port  162  may be connected to the compressor  15 . The second port  162  may be connected to the discharge side  15   b  of the compressor  15  through a refrigerant pipe  187 . The third port  163  may be connected to the indoor units  20  and  30  through refrigerant pipes  185 ,  183 , and  184 . The fourth port  164  may be connected to the outdoor heat exchanger  11 . The fourth port  164  may, be connected to the outdoor heat exchanger  11  through a refrigerant pipe  188 . 
     The outdoor expansion valve  17  may expand the refrigerant under reduced pressure. For example, the outdoor expansion valve  17  may be an electronic expansion valve (EEV) capable of adjusting the flow rate of a refrigerant. The EEV may control the flow rate of a refrigerant by adjusting the opening degree. 
     The refrigerant pipe P 1  of the outdoor unit  10  may include one or more refrigerant pipes  180 ,  181 ,  182 ,  183 ,  184 ,  185 ,  186 ,  187 , and  188 . 
     The refrigerant pipe  180  may be provided on one side of the outdoor heat exchanger  11 . For example, in a cooling mode, the refrigerant pipe  180  may be a pipe provided on a downstream side of the outdoor heat exchanger  11  and through which a refrigerant discharged from the outdoor heat exchanger  11  flows. For example, in a heating operation mode, the refrigerant pipe  180  may be a pipe provided on an upstream side of the outdoor heat exchanger  11  and through which a refrigerant sucked into the outdoor heat exchanger  11  flows. 
     The first outdoor pipe  181  and the second outdoor pipe  182  may be branched from the refrigerant pipe  180 . 
     The first outdoor pipe  181  may have an outdoor expansion valve  17  disposed thereon. The first outdoor pipe  181  may allow the refrigerant discharged from the outdoor heat exchanger  11  to pass through the outdoor expansion valve  17  and flow to the first indoor unit  20 . 
     The second outdoor pipe  182  may not have an outdoor expansion valve  17  disposed thereon. The second outdoor pipe  182  may allow the refrigerant discharged from the outdoor heat exchanger  11  to bypass the outdoor expansion valve  17  and flow to the second indoor unit  30 . 
     The refrigerant discharged from the first indoor unit  20  may flow into the third outdoor pipe  183 . The refrigerant discharged from the second indoor unit  30  may flow into the fourth outdoor pipe  184 . 
     The third outdoor pipe  183  and the fourth outdoor pipe  184  may be provided to join before being introduced into the compressor  15 . For example, the third outdoor pipe  183  and the fourth outdoor pipe  184  may join before being introduced into the third port  163  of the four-way valve  16  to form the refrigerant pipe  185 . 
     The refrigerant pipe  185  may be provided on one side of the compressor  15 . The refrigerant pipe  185  may be provided to be connected to the third port  163  of the four-way valve  16 . The refrigerant pipe  185  may be connected to the third outdoor pipe  183  and the fourth outdoor pipe  184 . For example, in a cooling mode, the refrigerant pipe  185  may be a pipe provided on an upstream side of the compressor  15  and through which the refrigerant discharged from the indoor units  20  and  30  flows. For example, in a heating operation mode, the refrigerant pipe  185  may be a pipe provided on a downstream side of the compressor  15  and through which the refrigerant discharged from the compressor  15  flows. 
     The refrigerant pipe  186  may connect the four-way valve  16  to the compressor  15 . The refrigerant pipe  186  may connect the first port  161  of the four-way valve  16  to the suction side  15   a  of the compressor  15 . 
     The refrigerant pipe  187  may connect the four-way valve  16  to the compressor  15 . The refrigerant pipe  187  may connect the second port  162  of the four-way valve  16  to the discharge side  15   b  of the compressor  15 . 
     The refrigerant pipe  188  may connect the outdoor heat exchanger  11  to the fourth port  164  of the four-way valve  16 . The refrigerant pipe  188  may be a pipe through which a refrigerant flows between the outdoor heat exchanger  11  and the compressor  15 . 
     The outdoor unit  10  may include a first connection valve  110  and a second connection valve  120 . The first connection valve  110  may connect the first outdoor pipe  181  to a first connection pipe  41  to be described below. The second connection valve  120  may connect the second outdoor pipe  182  to a second connection pipe  42  to be described below. 
     For example, in a cooling operation mode, the first connection valve  110  and the second connection valve  120  may control the amount of refrigerant discharged from the outdoor heat exchanger  11 . In this case, the first connection valve  110  and the second connection valve  120  may be referred to as exit valves of the outdoor unit  10 . 
     For example, in a heating operation mode, the first connection valve  110  and the second connection valve  120  may control the amounts of refrigerant introduced from the first indoor unit  20  and the second indoor unit  30 , respectively. In this case, the first connection valve  110  and the second connection valve  120  may be referred to as entry valves of the outdoor unit  10 . 
     The outdoor unit  10  may include a third connection valve  130  and a fourth connection valve  140 . The third connection valve  130  may connect the third outdoor pipe  183  to a third connection pipe  43  to be described below. The fourth connection valve  140  may connect the fourth outdoor pipe  184  to a fourth connection pipe  44  to be described below. 
     For example, in a cooling operation mode, the third connection valve  130  and the fourth connection valve  140  may control the amounts of refrigerant introduced from the first indoor unit  20  and the second indoor unit  30 , respectively. In this case, the third connection valve  130  and the fourth connection valve  140  may be referred to as entry valves of the outdoor unit  10 . 
     For example, in a heating operation mode, the third connection valve  130  and the fourth connection valve  140  may control the amount of refrigerant discharged from the compressor  15 . In this case, the third connection valve  130  and the fourth connection valve  140  may be referred to as exit valves of the outdoor unit  10 . 
     The first indoor unit  20  may be an indoor unit not having an indoor expansion valve. For example, the first indoor unit  20  may include a household indoor unit in which an indoor expansion valve is not built-in. When considering that a household indoor unit is generally installed in a residential space, the household indoor unit may not be provided with an indoor expansion valve to prevent an influence of noise generated during a reduced-pressure expansion process of a refrigerant. 
     The first indoor unit  20  may include the first indoor heat exchanger  21 . The first indoor heat exchanger  21  may be provided indoors to perform heat exchange between indoor air and a refrigerant. The first indoor heat exchanger  21  may be provided as an evaporator for evaporating a refrigerant in a cooling operation mode, and may be provided as a condenser for condensing a refrigerant in a heating operation mode. 
     The first indoor unit  20  may include a fan motor  22  and an indoor fan  23  (see  FIG.  7   ). The indoor fan  23  may forcibly blow indoor air so that heat exchange between the indoor air and the refrigerant is performed in the first indoor heat exchanger  21 . The indoor fan  23  may be driven by the fan motor  22 . 
     The first indoor unit  20  may include a refrigerant pipe P 2 , i.e.,  24  and  25 . The refrigerant pipe P 2  of the first indoor unit  20  may be provided as a plurality of refrigerant pipes  24  and  25 . 
     The refrigerant pipe  24  may be provided at a first side of the first indoor heat exchanger  21 , and the refrigerant pipe  25  may be provided at a second side of the first indoor heat exchanger  21 . 
     For example, in a cooling operation mode, the refrigerant pipe  24  may be provided on an upstream side of the first indoor heat exchanger  21 , and the refrigerant pipe  25  may be provided on a downstream side of the first indoor heat exchanger  21 . 
     For example, in a heating operation mode, the refrigerant pipe  24  may be provided on a downstream side of the first indoor heat exchanger  21 , and the refrigerant pipe  25  may be provided on an upstream side of the first indoor heat exchanger  21 . 
     The first indoor unit  20  may include connection valves  26  and  27 . The connection valves  26  and  27  of the first indoor unit  20  may be provided in plural. 
     The connection valve  26  may connect the first connection pipe  41 , which will be described below, to the refrigerant pipe  24 . The connection valve  27  may connect the third connection pipe  43 , which will be described below, to the refrigerant pipe  25 . 
     For example, in a cooling operation mode, the connection valve  26  may control the amount of refrigerant introduced from the outdoor unit  10 . In this case, the connection valve  26  may be referred to as an entry valve of the first indoor unit  20 . For example, in a heating operation mode, the connection valve  26  may control the amount of refrigerant discharged from the first indoor unit  20 . In this case, the connection valve  26  may be referred to as an exit valve of the first indoor unit  20 . 
     For example, in a cooling operation mode, the connection valve  27  may control the amount of refrigerant discharged from the first indoor unit  20 . In this case, the connection valve  27  may be referred to as an exit valve of the first indoor unit  20 . For example, in a heating operation mode, the connection valve  27  may control the amount of refrigerant introduced from the outdoor unit  10 . In this case, the connection valve  27  may be referred to as an entry valve of the first indoor unit  20 . 
     The second indoor unit  30  may be an indoor unit provided with an indoor expansion valve  38 . For example, the second indoor unit  30  may include a commercial indoor unit in which the indoor expansion valve  38  is built-in. In general, since a commercial indoor unit includes a pipe between the outdoor unit and the indoor unit having a length longer than that of a household indoor unit, an expansion valve may be provided in the indoor unit to compensate for a pressure loss due to the long pipe. 
     The indoor expansion valve  38  may expand the refrigerant under reduced pressure. For example, the indoor expansion valve  38  may be an electronic expansion valve (EEV) capable of adjusting the flow rate of a refrigerant. The EEV may control the flow rate of the refrigerant by adjusting the opening degree. 
     The second indoor unit  30  may include a second indoor heat exchanger  31 . The second indoor heat exchanger  31  may be provided indoors to perform heat exchange between indoor air and a refrigerant. The second indoor heat exchanger  31  may be provided as an evaporator for evaporating a refrigerant in a cooling operation mode, and may be provided as a condenser for condensing a refrigerant in a heating operation mode. 
     The second indoor unit  30  may include a fan motor  32  and an indoor fan  33  (see  FIG.  7   ). The indoor fan  33  may force the indoor air to be blown so that heat exchange between the indoor air and the refrigerant is performed in the second indoor heat exchanger  31 . The indoor fan  33  may be driven by the fan motor  32 . 
     The second indoor unit  30  may include a refrigerant pipe P 3 , i.e.,  34  and  35 , The refrigerant pipe P 3  may be provided as a plurality of refrigerant pipes  34  and  35 . 
     The second indoor unit  30  may include a refrigerant pipe P 3 , i.e.,  34  and  35 . The refrigerant pipe P 2  of the second indoor unit  30  may be provided as a plurality of indoor units  34  and  35 . 
     The refrigerant pipe  34  may be provided on a first side of the second indoor heat exchanger  31 , and the refrigerant pipe  35  may be provided on a second side of the second indoor heat exchanger  31 . 
     For example, in a cooling operation mode, the refrigerant pipe  34  may be provided on an upstream side of the second indoor heat exchanger  31 , and the refrigerant pipe  35  may be provided on a downstream side of the second indoor heat exchanger  31 . 
     For example, in a heating operation mode, the refrigerant pipe  34  may be provided on a downstream side of the second indoor heat exchanger  31 , and the refrigerant pipe  35  may be provided on an upstream side of the second indoor heat exchanger  31 . 
     The indoor expansion valve  38  of the second indoor unit  30  may be disposed in the refrigerant pipe  34 . For example, the refrigerant discharged from the outdoor heat exchanger  11  and bypassing the outdoor expansion valve  17  may pass through the indoor expansion valve  38  and flow into the second indoor heat exchanger  31 . 
     The second indoor unit  30  may include connection valves  36  and  37 . The connection valves  36  and  37  of the second indoor unit  30  may be provided in plural. 
     The connection valve  36  may connect the second connection pipe  42 , which will be described below, to the refrigerant pipe  34 . The connection valve  37  may connect the fourth connection pipe  44 , which will be described below, to the refrigerant pipe  35 . 
     For example, in a cooling operation mode, the connection valve  36  may adjust the amount of refrigerant introduced from the outdoor unit  10 . In this case, the connection valve  36  may be referred to as an entry valve of the second indoor unit  30 . For example, in a heating operation mode, the connection valve  36  may adjust the amount of refrigerant discharged from the second indoor unit  30 . In this case, the connection valve  36  may be referred to as an exit valve of the second indoor unit  30 . 
     For example, in a cooling operation mode, the connection valve  37  may adjust the amount of refrigerant discharged from the second indoor unit  30 . In this case, the connection valve  37  may be referred to as an exit valve of the second indoor unit  30 . For example, in a heating operation mode, the connection valve  37  may adjust the amount of refrigerant introduced from the outdoor unit  10 . In this case, the connection valve  37  may be referred to as an entry valve of the second indoor unit  30 . 
     The connection pipe  40  may connect the outdoor unit  10  to the indoor units  20  and  30 . 
     For example, the connection pipe  40  may include the first connection pipe  41 , the second connection pipe  42 , the third connection pipe  43 , and the fourth connection pipe  44 . 
     Each of the first connection pipe  41  and the third connection pipe  43  may be provided to connect the outdoor unit  10  to the first indoor unit  20 . Each of the second connection pipe  42  and the fourth connection pipe  44  may be provided to connect the outdoor unit  10  to the second indoor unit  30 . 
     The first connection pipe  41  may connect the first outdoor pipe  181  of the outdoor unit  10  to the refrigerant pipe  24  of the first indoor unit  20 . The first connection valve  110  of the outdoor unit  10  may connect the first outdoor pipe  181  to the first connection pipe  41 . The connection valve  26  of the first indoor unit  20  may connect the first connection pipe  41  to the refrigerant pipe  24 . 
     The first connection pipe  41  may connect the first outdoor pipe  181  provided with the outdoor expansion valve  17  to the first indoor unit  20  not provided with an indoor expansion valve. 
     The second connection pipe  42  may connect the second outdoor pipe  182  of the outdoor unit  10  to the refrigerant pipe  34  of the second indoor unit  30 . The second connection valve  120  of the outdoor unit  10  may connect the second outdoor pipe  182  to the second connection pipe  42 . The connection valve  36  of the second indoor unit  30  may connect the second connection pipe  42  to the refrigerant pipe  34 . 
     The second connection pipe  42  may connect the second outdoor pipe  182  not provided with an outdoor expansion valve to the second indoor unit  30  provided with the indoor expansion valve  38 . 
     The third connection pipe  43  may connect the refrigerant pipe  25  of the first indoor unit  20  to the third outdoor pipe  183  of the outdoor unit  10 . The third connection valve  130  of the outdoor unit  10  may connect the third connection pipe  43  to the third outdoor pipe  183 . The connection valve  27  of the first indoor unit  20  may connect the refrigerant pipe  25  to the third connection pipe  43 . 
     The fourth connection pipe  44  may connect the refrigerant pipe  35  of the second indoor unit  30  to the fourth outdoor pipe  184  of the outdoor unit  10 . The fourth connection valve  140  of the outdoor unit  10  may connect the fourth connection pipe  44  to the fourth outdoor pipe  184 . The connection valve  37  of the second indoor unit  30  may connect the refrigerant pipe  35  to the fourth connection pipe  44 . 
     The refrigerant pipe P 1  of the outdoor unit  10 , the refrigerant pipe P 2  of the first indoor unit  20 , the refrigerant pipe P 3  of the second indoor unit  30 , and the connection pipe  40  may form a refrigerant cycle in which a refrigerant circulates. The refrigerant cycle may be provided as a closed loop. 
     As described above, both the indoor unit  20  not provided with an indoor expansion valve and the indoor unit  30  provided with an indoor expansion valve may be connected to the outdoor unit  10 . That is, the air conditioner  1  may implement both a single-pipe structure and a multi-pipe structure. 
     In general, an air conditioner may be provided in a single pipe structure or a multi-pipe structure. The single pipe structure is a structure in which an outdoor unit not having an outdoor expansion valve is connected through a branch pipe to indoor units (e.g., a commercial indoor unit) having indoor expansion valves. The multi-pipe structure is a structure in which an outdoor unit having an outdoor expansion valve is connected to indoor units (e.g., a residential indoor unit), which do not have indoor expansion valves, through separate pipes. For example, an air conditioner having a single pipe structure may be used in a commercial area, and an air conditioner having a multi pipe structure may be used in a residential area. 
     Recently, as commercial areas and residential areas are mixed, there is a need for a technology capable of installing both an indoor unit with built-in indoor expansion valve (e.g., a commercial indoor unit) and an indoor unit without a built-in indoor expansion valve (e.g., a residential indoor unit). However, since the air conditioner having a single pipe structure and the air conditioner having a multi pipe structure have different internal configurations and pipe designs, it is difficult to implement the air conditioners as a single system, and separate parts and the like are required. For example, when a household indoor unit without a built-in expansion valve needs to be additionally installed in an air conditioner having a single pipe structure, a separate distribution device having an expansion valve may be required. Accordingly, a space for installing separate parts and the like needs to be secured, and piping design may become very complicated to connect the separate parts and the like. 
     The disclosed air conditioner  1  may implement both a single-pipe structure and a multi-pipe structure through a simple piping design. 
     The outdoor unit  10  of the air conditioner  1  may include the first outdoor pipe  181  in which the outdoor expansion valve  17  is provided and the second outdoor pipe  182  in which the outdoor expansion valve  17  is not provided. The first indoor unit  20  may be connected to the first outdoor pipe  181  through the first connection pipe  41 , and the second indoor unit  30  may be connected to the second outdoor pipe  182  through the second connection pipe  42 . Accordingly, both the first indoor unit  20  not having a built-in indoor expansion valve and the second indoor unit  30  having a built-in indoor expansion valve may be connectable to the outdoor unit  10 . 
     The refrigerant discharged from the outdoor heat exchanger  11  may pass through the refrigerant pipe  180  and branch into the first outdoor pipe  181  and the second outdoor pipe  182 . 
     The refrigerant introduced into the first outdoor pipe  181  may pass through the outdoor expansion valve  17 , and then through the first connection pipe  41 , flow into the first indoor heat exchanger  21  of the first indoor unit  20 . The refrigerant flowing into the first indoor heat exchanger  21  may be a refrigerant expanded under reduced pressure via the outdoor expansion valve  17 . 
     The refrigerant introduced into the second outdoor pipe  182  may not pass through the outdoor expansion valve  17 , but pass through the second connection pipe  42 , flowing into the indoor expansion valve  38  of the second indoor unit  30 . The refrigerant expanded under reduced pressure through the indoor expansion valve  38  may be introduced into the second indoor heat exchanger  31 . 
     With such a configuration, both an indoor unit having an indoor expansion valve (e.g., a commercial indoor unit) and an indoor unit not having an indoor expansion valve (e.g., a residential indoor unit) may be installable in the outdoor unit  10 . That is, both the first indoor unit and the second indoor unit of different types may be connectable to the outdoor unit regardless of whether the indoor unit has an indoor expansion valve (e.g., an EEV) built-in. Accordingly, the air conditioner  1  may implement one system in which a single pipe structure and a multi-pipe structure are integrated. In addition, since the air conditioner  1  does not require a separate component (e.g., a distribution device), installation restrictions may be eliminated and piping design may be simplified. 
     Meanwhile, the first connection valve  110  and the second connection valve  120  of the air conditioner  1  may be provided to be identifiable from each other. Accordingly, it is possible to prevent in advance an accident, such as an operator erroneously connecting the first indoor unit  20  and the second indoor unit  30  to the outdoor unit. For example, the first indoor unit  20  needs to be connected to the first outdoor pipe  181  through the first connection pipe  41 , and the second indoor unit  30  needs to be connected to the second outdoor pipe  182  through the second connection pipe  42 . 
     For example, the first connection valve  110  and the second connection valve  120  may be provided to be different in at least one of a shape, form, size, and color thereof. Since the first connection valve  110  and the second connection valve  120  are provided to be different from each other, mutual identification may be facilitated. 
     A mark for identifying the first connection valve  110  and the second connection valve  120  may be provided. For example, only one of the first connection valve  110  and the second connection valve  120  may be marked, or a mark formed on the first connection valve  110  and a mark formed on the second connection valve  120  may be provided to be different from each other. For example, only one of the first connection valve  110  and the second connection valve  120  may be subject to imprinting, or the imprint on the first connection valve  110  and the imprint of the second connection valve  120  may be different from each other. 
     A valve marker  170  for indicating a connection state of the first connection valve  110  and the second connection valve  120  may be provided. For example, the valve marker  170  may indicate that the first outdoor pipe  181  need to be connected to the first connection valve  110  and the second outdoor pipe  182  need to be connected to the second connection valve  120 . 
     For example, the valve marker  170  may include a first valve marker  171  corresponding to the first connection valve  110  and may include a second valve marker  172  corresponding to the second connection valve  120 . For example, the first valve marker  171  and the second valve marker  172  may include a lighting unit, such as a light emitting diode (LED), and the lighting unit of the first valve marker  171  and the lighting unit of the second valve marker  172  may be provided to present different colors. 
     However, it is not limited to the above-described examples, and various methods of identifying the first connection valve  110  and the second connection valve  120  may be adopted. 
     The third connection valve  130  and the fourth connection valve  140  maybe provided to be identifiable from each other. Similar to the first connection valve  110  and the second connection valve  120 , various methods of mutually identifying the third connection valve  130  and the fourth connection valve  140  may be adopted. 
     With reference to  FIG.  2   , an embodiment of an air conditioner  1  in which a plurality of first indoor units  20  and one second indoor unit  30  are connected to an outdoor unit  10  will be described. In  FIG.  2   , the first indoor unit  20  is illustrated as two indoor units, but the disclosure is not limited thereto, and the first indoor unit  20  may be provided as two or more indoor units. The same reference numerals are assigned to the same configurations, and the same descriptions as those of  FIG.  1    may be omitted. 
     Compared with the embodiment shown in  FIG.  1   , the first indoor unit  20  may be provided in plural. Referring to  FIG.  2   , the first indoor unit  20  may include a first a-indoor unit  20   a  and a first b-indoor unit  20   b.    
     Each of the first outdoor pipe  181 , the first connection valve  110 , and the first connection pipe  41  may be provided in plural to correspond to the first indoor units  20 . Each of the first outdoor pipe  181 , the first connection valve  110 , and the first connection pipe  41  may be provided corresponding in number to the number of the first indoor units  20 . 
     For example, referring to  FIG.  2   , the first outdoor pipe  181  may include a first a-outdoor pipe  181   a  and a first-b outdoor pipe  181   b . The outdoor expansion valve  17  may include a first outdoor expansion valve  17   a  disposed on the first a-outdoor pipe  181   a  and a second outdoor expansion valve  17   b  disposed on the first b-outdoor pipe  181   b . The first connection pipe  41  may include a first a-connection pipe  41   a  and a first b-connection pipe  41   b . The first connection valve  110  may include a first a-connection valve  110   a  and a first b-connection valve Hob. 
     The first outdoor pipes  181 , the first connection valves  110 , and the first connection pipes  41  may be respectively connected in series to form a plurality of refrigerant lines. 
     For example, the first a-outdoor pipe  181   a , the first a-connection valve  110   a , and the first a-connection pipe  41   a  may form a first refrigerant line. For example, the first b-outdoor pipe  181   b , the first b-connection valve  110   b , and the first b-connection pipe  41   b  may form a second refrigerant line. 
     Each of the first indoor units  20  may be connected to the outdoor heat exchanger  11  while corresponding to a respective one of the plurality of refrigerant lines. For example, the first a-indoor unit  20   a  may be connected to the outdoor heat exchanger  11  through the first refrigerant line, and the first b-indoor unit  20   b  may be connected to the outdoor heat exchanger  11  through the second refrigerant line. 
     Some portion of the refrigerant discharged from the outdoor heat exchanger  11  may flow into the first a-outdoor pipe  181   a  and pass through the first outdoor expansion valve  17   a . The refrigerant discharged from the first a-outdoor pipe  181   a  may pass through the first a-connection valve  110   a  and the first a-connection pipe  41   a  to be introduced into a first a-indoor heat exchanger  21   a.    
     Another portion of the refrigerant discharged from the outdoor heat exchanger  11  may flow into the first b-outdoor pipe  181   b  and pass through the second outdoor expansion valve  17   b . The refrigerant discharged from the first b-outdoor pipe  181   b  nay pass through the first b-connection valve  110   b  and the first b-connection pipe  41   b  to be introduced into a first b-indoor heat exchanger  21   b.    
     The remaining of the refrigerant discharged from the outdoor heat exchanger  11  may flow into the second outdoor pipe  182  and pass through the second connection valve  120  and the second connection pipe  42 . The refrigerant passing through the second connection valve  120  and the second connection pipe  42  may pass through the indoor expansion valve  38  to be introduced into the second indoor heat exchanger  31 . 
     Each of the third connection pipe  43 , the third connection valve  130 , and the third outdoor pipe  183  may also be provided in plural to correspond to the first indoor units  20 . Each of the third connection pipe  43 , the third connection valve  130 , and the third outdoor pipe  183  may be provided corresponding in number to the number of the first indoor units  20 . 
     For example, the third connection pipe  43  may include a third a-connection pipe  43   a  and a third b-connection pipe  43   b . The third connection valve  130  may include a third a-connection valve  130   a  and a third b-connection valve  130   b . The third outdoor pipe  183  may include a third-a outdoor pipe  183   a  and a third b-outdoor pipe  183   b.    
     The first a-indoor unit  20   a , the third a-connection pipe  43   a , the third a-connection valve  130   a , and the third a-outdoor pipe  183   a  may be connected in series. The first b-indoor unit  20   b , the third connection valve  43   b , the third b-connection valve  130   b , and the third b-outdoor pipe  183   b  may be connected in series. 
     An embodiment of an air conditioner  1  in which one first indoor unit  20  and a plurality of second indoor units  30  are connected to an outdoor unit  10  will be described with reference to  FIG.  3   . In  FIG.  3   , the second indoor unit  30  is illustrated as two second indoor units, but the disclosure is not limited thereto, and the second indoor unit  30  may be provided as two or more second indoor units. The same reference numerals are assigned to the same configurations, and the same descriptions as those of  FIGS.  1  and  2    may be omitted. 
     Compared with the embodiment shown in  FIG.  1   , the second indoor unit  30  may be provided in plural. Referring to  FIG.  3   , the second indoor unit  30  may include a second a-indoor unit  30   a  and a second b-indoor unit  30   b , The second a-indoor unit  30   a  may include a second a-indoor heat exchanger  31   a  and a first indoor expansion valve  38   a . The second b-indoor unit  30   b  may include a second b-indoor heat exchanger  31   b  and a second indoor expansion valve  38   b.    
     The second connection pipe  42  may include one main connection pipe  421  provided to be connected to the second connection valve  120  and a plurality of sub connection pipes  422   a  and  422   b  branched from the main connection pipe  421 . The plurality of sub connection pipes  422   a  and  422   b  may be provided to correspond to the plurality of second indoor units  30   a  and  30   b , respectively. The plurality of sub connection pipes  422   a  and  422   b  may be provided corresponding in number to the number of the second indoor unit  30 . 
     For example, referring to  FIG.  3   , the plurality of sub connection pipes may include a first sub connection pipe  422   a  connected to the second a-indoor unit  30   a  and a second sub connection pipe  422   b  connected to the second b-indoor unit  30   b.    
     Some portion of the refrigerant discharged from the outdoor heat exchanger  11  may flow into the first outdoor pipe  181  and pass through the outdoor expansion valve  17 . The refrigerant discharged from the first outdoor pipe  181  may pass through the first connection valve  110  and the first connection pipe  41  to be introduced into the first indoor heat exchanger  21 . 
     The remaining of the refrigerant discharged from the outdoor heat exchanger  11  may flow into the second outdoor pipe  182  and pass through the second connection valve  120 . The refrigerant discharged from the second connection valve  120  may flow through the main connection pipe  421  and branch through the sub connection pipes  422   a  and  422   b.    
     The refrigerant flowing into the first sub-connection pipe  422   a  may pass through the first indoor expansion valve  38   a  and flow into the second a-indoor heat exchanger  31   a . The refrigerant flowing into the second sub connection pipe  422   b  may pass through the second indoor expansion valve  38   b  and flow into the second b-indoor heat exchanger  31   b.    
     The fourth connection pipe  44  may include a plurality of sub connection pipes  442   a  and  442   b  connected to the plurality of second indoor units  30   a  and  30   b , respectively, and a main connection pipe  441  in which the plurality of sub connection pipes  442   a  and  442   b  join. The main connection pipe  441  may be connected to the fourth connection valve  140 . 
     The refrigerants discharged from the plurality of second indoor units  30   a  and  30   b  may flow along the respective sub-connection pipes  442   a  and  442   b . The refrigerants flowing through the respective sub-connection pipes  442   a  and  442   b  may join in the main connection pipe  441 . The refrigerant joining in the main connection pipe  441  may pass through the fourth connection valve  140  and flow into the fourth outdoor pipe  184 . 
     With reference to  FIG.  4   , an embodiment of an air conditioner  1  in which a plurality of first indoor units  20  and a plurality of second indoor units  30  are connected to an outdoor unit  10  will be described. In  FIG.  4   , the first indoor unit  20  is illustrated as two first indoor units  20  and the second indoor unit  30  is illustrated as two second indoor units  30 , but the disclosure is not limited thereto. The first indoor unit  20  may be provided as two or more first indoor units  20 , and the second indoor unit  30  may be provided as two or more second indoor units  30 . The same reference numerals are assigned to the same configurations, and the same descriptions as those of  FIGS.  1  to  3    may be omitted. 
     Referring to  FIG.  4   , the outdoor unit  10  may be connected to the plurality of first indoor units  20  and the plurality of second indoor units  30 . The air conditioner  1  may be provided in a structure in which a multi-pipe structure and a single-pipe structure are integrated. 
     For example, the first a-outdoor pipe  181   a , the first a-connection valve  110   a , the first a-connection pipe  41   a , and the first a-indoor unit  20   a  may be connected in series. The first b-outdoor pipe  181   b , the first b-connection valve  110   b , the first b-connection pipe  41   b , and the first b-indoor unit  20   b  may be connected in series. The first a-indoor unit  20   a , the third a-connection pipe  43   a , the third a-connection valve  130   a , and the third a-outdoor pipe  183   a  may be connected in series. The first b-indoor unit  20   b , the third connection pipe  43   b , the third b-connection valve  130   b , and the third b-outdoor pipe  183   b  may be connected in series. That is, with such a connection, a multi-pipe structure may be provided. 
     For example, the sub connection pipe  422   a , the second a-indoor unit  30   a , and the sub connection pipe  442   a  may be connected in series (hereinafter, referred to as a first connection part). The sub connection pipe  422   b , the second b-indoor unit  30   b , and the sub connection pipe  442   b  may be connected in series (hereinafter, referred to as a second connection part). The first connection part and the second connection part may be connected in parallel to each other. That is, the plurality of sub connection pipes  422   a  and  422   b  branched from the main connection pipe  421  are connected to the plurality of second indoor units  30   a  and  30   b , respectively, and the plurality of sub connection pipes  442   a  and  442   b  extending from the plurality of second indoor units  30   a  and  30   b  may join at the main connection pipe  441 . That is, with such a connection, a single pipe structure may be provided. 
     The first indoor units  20   a  and  20   b  not provided with an indoor expansion valve may be respectively connected to the first outdoor pipes  181   a  and  181   b  in which the outdoor expansion valves  17   a  and  17   b  are disposed. The second indoor units  30   a  and  30   b  provided with the indoor expansion valves may be connected to the second outdoor pipe  182  in which the outdoor expansion valves  17   a  and  17   b  are not disposed. For example, the second indoor units  30   a  and  30   b  may be connected to the second outdoor pipe  182  through the branch pipes  422   a  and  422   b , respectively. 
     As described above, the air conditioner  1  may be provided in a structure in which a multi-pipe structure and a single-pipe structure are integrated. Accordingly, the indoor units  20  and  30  may be connected to the outdoor unit  10  regardless of whether the indoor unit has an expansion valve built-in. In addition, since a separate distribution device is not required, the piping design is simplified, which is beneficial in space securing. 
       FIG.  5    is a diagram schematically illustrating a cooling operation mode of the air conditioner shown in  FIG.  1   . 
     Referring to  FIG.  5   , in a cooling operation mode, a refrigerant may be circulated in the order of the compressor  15 , the four-way valve  16 , the outdoor heat exchanger  11 , and the indoor units  20  and  30 . In this case, the outdoor heat exchanger  11  may serve as a condenser, and the first indoor heat exchanger  21  and the second indoor heat exchanger  22  may serve as an evaporator. 
     The four-way valve  16  may connect the first port  161  to the third port  163  and connect the second port  162  to the fourth port  164 . 
     The refrigerant compressed in the compressor  15  may be introduced into the outdoor heat exchanger  11  by the four-way valve  16 . The refrigerant heat-exchanged with outdoor air in the outdoor heat exchanger  11  may flow toward the indoor units  20  and  30 . 
     The refrigerant discharged from the outdoor heat exchanger  11  may be branched through the first outdoor pipe  181  and the second outdoor pipe  182 . 
     The refrigerant flowing into the first outdoor pipe  181  may pass through the outdoor expansion valve  17 . The refrigerant passing through the outdoor expansion valve  17  may pass through the first connection valve  110  and the first connection pipe  41  to be introduced into the first indoor heat exchanger  21 . The refrigerant heat-exchanged with the indoor air in the first indoor heat exchanger  21  may pass through the third connection pipe  43  and the third connection valve  130  to be introduced into the four-way valve  16 . The refrigerant passed through the four-way valve  16  may be introduced back into the compressor  15 . 
     The refrigerant introduced into the second outdoor pipe  182  may bypass the outdoor expansion valve  17 . The refrigerant bypassing the outdoor expansion valve  17  may pass through the second connection valve  120  and the second connection pipe  42  to flow into the indoor expansion valve  38 . The refrigerant expanded under reduced pressure in the indoor expansion valve  38  may be introduced into the second indoor heat exchanger  31 . The refrigerant heat-exchanged with the indoor air in the second indoor heat exchanger  31  may pass through the fourth connection pipe  44  and the fourth connection valve  140  and then flow into the four-way valve  16 . The refrigerant passed through the four-way valve  16  may be introduced back into the compressor  15 . 
       FIG.  6    is a diagram schematically illustrating a heating operation mode of the air conditioner shown in  FIG.  1   . 
     Referring to  FIG.  6   , in a heating operation mode, the refrigerant may be circulated in the order of the compressor  15 , the four-way valve  16 , the indoor units  20  and  30 , and the outdoor heat exchanger  11 . In this case, the outdoor heat exchanger  11  may serve as an evaporator, and the first indoor heat exchanger  21  and the second indoor heat exchanger  31  may serve as a condenser. 
     The four-way valve  16  may connect the first port  161  to the fourth port  164  and connect the second port  162  to the third port  163 . 
     The refrigerant compressed in the compressor  15  may be caused to flow toward the indoor units  20  and  30  by the four-way valve  16 . 
     The refrigerant discharged from the four-way valve  16  may be branched through the third outdoor pipe  183  and the fourth outdoor pipe  184 . 
     The refrigerant introduced into the third outdoor pipe  183  may pass through the third connection valve  130  and the third connection pipe  43  to be introduced into the first indoor heat exchanger  21 . The refrigerant heat-exchanged with indoor air in the first indoor heat exchanger  21  may pass through the first connection pipe  41  and the first connection valve  110  and flow into the first outdoor pipe  181 . The refrigerant flowing into the first outdoor pipe  181  may pass through the outdoor expansion valve  17  to be introduced into the outdoor heat exchanger  11 . The refrigerant heat-exchanged with outdoor air in the outdoor heat exchanger  11  may be introduced back into the compressor  15  by the four-way valve  16 . 
     The refrigerant flowing into the fourth outdoor pipe  184  may pass through the fourth connection valve  140  and the fourth connection pipe  44  to be introduced into the second indoor heat exchanger  31 . The refrigerant heat-exchanged with indoor air in the second indoor heat exchanger  31  may pass through the indoor expansion valve  38  of the second indoor unit  20 . The refrigerant passed through the indoor expansion valve  38  may pass through the second connection pipe  42  and the second connection valve  120  to be introduced into the second outdoor pipe  182 . The refrigerant introduced into the second outdoor pipe  182  may be introduced into the outdoor heat exchanger  11 . The refrigerant heat-exchanged with outdoor air in the outdoor heat exchanger  11  may be introduced back into the compressor  15  by the four-way valve  16 . 
       FIG.  7    is a control block diagram illustrating an air conditioner according to an embodiment. 
     Referring to  FIG.  7   , the air conditioner  1  may include controllers  100 ,  200 , and  300  for controlling each component of the air conditioner  1 . For example, the outdoor unit  10  may include an outdoor unit controller  100 , the first indoor unit  20  may include a first indoor unit controller  200 , and the second indoor unit  30  may include a second indoor unit controller  300 . However, the disclosure is not limited thereto, and the outdoor unit controller  100 , the first indoor unit controller  200 , and the second indoor unit controller  300  may be integrated into one body. For example, some of the outdoor unit controller  100 , the first indoor unit controller  200 , and the second indoor unit controller  300  may be integrated into one body. 
     The outdoor unit controller  100  may control the operation of the outdoor unit  10 . The outdoor unit controller  100  may receive various types of information about the operation of the outdoor unit  10 , and control components of the outdoor unit  10  based on the received information. For example, the outdoor unit controller  100  may control the operation of the compressor  15 , the accumulator  14 , the fan motor  12 , the outdoor fan  13 , the four-way valve  16 , the outdoor expansion valve  17 , and the like. 
     The outdoor unit controller  100  may control the opening degree of the first connection valve  110 , the second connection valve  120 , the third connection valve  130 , and the fourth connection valve  140  to adjust the amount of refrigerant flowing in or flowing out of the indoor units  20  and  30 . 
     The outdoor unit controller  100  may control the valve marker  170 . The outdoor unit controller  100  may control the valve marker  170  so that the first connection valve  110  and the second connection valve  120  are mutually identified from each other. For example, the first valve marker  171  corresponding to the first connection valve  110  and the second valve marker  171  corresponding to the second connection valve  120  may be provided in different forms to be identified from each other. 
     Meanwhile, the outdoor unit controller  100  may control the third connection valve  130  and the fourth connection valve  140  to be mutually identified from each other. Although not shown in the drawing, the valve marker  170  may include a third valve marker (not shown) corresponding to the third connection valve  130  and a fourth valve marker (not shown) corresponding to the fourth connection valve  140 . In this case, the outdoor unit controller  100  may control the operations of the third valve marker and the fourth valve marker. 
     The outdoor unit  100  may further include an outdoor unit communicator  150 . The outdoor unit communicator  150  may be connected to the outdoor unit controller  100  and provided to communicate with the indoor units  20  and  30 . For example, the outdoor unit communicator  150  may be provided to communicate with a first indoor unit communicator  230  and a second indoor unit communicator  330 . For example, the outdoor unit communicator  150  may be provided to communicate with a user terminal (e.g., a mobile phone, a tablet, a personal computer (PC), etc.). 
     The outdoor unit communicator  150  may receive information on whether the indoor units  20  and  30  include an indoor expansion valve. For example, the outdoor unit communicator  150  may receive, from the first indoor unit communicator  230 , information about inclusion of an indoor expansion valve. The outdoor unit communicator  150  may receive, from the second indoor unit communicator  330 , information about inclusion of the indoor expansion valve  38 . 
     The outdoor unit controller  100  may be provided to control the valve marker  170  based on information received from the outdoor unit communicator  150 . For example, when the second indoor unit  30  is connected to the first connection valve  110  and the first indoor unit  20  is connected to the second connection valve  120 , the air conditioner  1  may inform the user that the pipe connection is incorrect through various methods (e.g., a warning sound, a LED lighting, etc.). In addition, when the second indoor unit  30  is connected to the third connection valve  130  and the first indoor unit  20  is connected to the fourth connection valve  140 , the air conditioner  1  may inform the user that the pipe connection is incorrect using various methods (e.g., a warning sound, a LED lighting, etc.). 
     The first indoor unit controller  200  may control the operation of the first indoor unit  20 . The first indoor unit controller  200  may control components of the first indoor unit  20 . For example, the first indoor unit controller  200  may control operations of the fan motor  22 , the indoor fan  23 , and the connection valves  26  and  27 . 
     The first indoor unit controller  200  may control the opening degrees of the connection valves  26  and  27  to adjust the amount of refrigerant flowing in or flowing out of the outdoor unit  10 . 
     The first indoor unit  20  may include an inputter  210 , a display  220 , and a first indoor unit communicator  230 . 
     The inputter  210  may be provided to receive information from a user. The display  220  may display the operating state of the first indoor unit  20 . The inputter  210  and the display  220  may be provided separately, or may be integrated into one body and provided as a user interface (at UI). The inputter  210  and the display  220  may be connected to the first indoor unit controller  200 . 
     The first indoor unit communicator  230  may be connected to the first indoor unit controller  200  and provided to communicate with the outdoor unit communicator  150 . For example, the first indoor unit communicator  230  may transmit, to the outdoor unit communicator  150 , information on whether the first indoor unit  20  includes an indoor expansion valve. 
     The second indoor unit controller  300  may control the operation of the second indoor unit  30 . The second indoor unit controller  300  may control components of the second indoor unit  30 . For example, the second indoor unit controller  300  may control operations of the fan motor  32 , the indoor fan  33 , the connection valves  36  and  37 , and the indoor expansion valve  38 . 
     The second indoor unit controller  300  may control the opening degrees of the connection valves  36  and  37  to adjust the amount of refrigerant flowing in or flowing out of the outdoor unit  10 . 
     The second indoor unit  30  may include an inputter  310 , a display  320 , and a second indoor unit communicator  330 . 
     The inputter  310  may be provided to receive information from a user. The display  320  may display the operating state of the second indoor unit  30 . The inputter  310  and the display  320  may be provided separately, or may be integrated into one body and provided as a user interface (an UI). The inputter  310  and the display  320  may be connected to the second indoor unit controller  300 . 
     The second indoor unit communicator  330  may be connected to the second indoor unit controller  300  and provided to communicate with the outdoor unit communicator  150 , For example, the first indoor unit communicator  330  may transmit, to the outdoor unit communicator  150 , information on whether the second indoor unit  30  includes the indoor expansion valve  38 . 
     One aspect of the disclosure provides an air conditioner having an improved refrigerant pipe structure. 
     Another aspect of the disclosure provides an air conditioner including an outdoor unit connectable to both an indoor unit having an expansion valve built-in and an indoor unit not having an expansion valve built-in. 
     Another aspect of the disclosure provides an air conditioner capable of implementing both a single pipe structure and a multi-pipe structure. 
     According to one aspect of the disclosure, the air conditioner can easily connect an indoor unit to are outdoor unit regardless of whether an expansion valve is included in the indoor unit. 
     According to one aspect of the disclosure, the air conditioner can combine a single pipe structure and a multi-pipe structure. 
     According to one aspect of the disclosure, the air conditioner can easily install an indoor unit without a separate distribution device. 
     Although certain illustrative embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this description. Accordingly, the inventive concepts are not limited to such embodiments, but rather to the broader scope of the appended claims and various obvious modifications and equivalent arrangements as would be apparent to a person of ordinary skill in the art.