Abstract:
An air conditioner includes a compressor, first and second heat exchangers connected with high pressure piping, low pressure piping connecting the second heat exchanger to a compressor suction port, a pressure reducing mechanism arranged to reduce pressure in the high pressure piping, a bypass passageway, a vessel connected to the bypass passageway, and first and second opening/closing mechanisms. The first heat exchanger is connected to a compressor discharge port. The bypass passageway is arranged to divert refrigerant from the high pressure piping to the low pressure piping without passing through the second heat exchanger. The first opening/closing mechanism is arranged to open/close a first portion of the bypass passageway that connects the high pressure piping to the vessel. The second opening/closing mechanism is arranged to open/close a second portion of the bypass passageway that connects an upper part of the vessel to the low pressure piping.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2007-143814, filed in Japan on May 30, 2007, the entire contents of which are hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an air conditioner that can determine whether a refrigerant circuit is filled with the appropriate amount of refrigerant. 
     BACKGROUND ART 
     In the conventional art, an air conditioner that comprises a heat source unit, a utilization unit, and a connection piping, which connects the heat source unit and the utilization unit, is known. When this air conditioner is constructed, a procedure is performed onsite wherein a refrigerant circuit of the air conditioner is filled with a refrigerant. 
     Nevertheless, if the refrigerant circuit is filled with an amount of refrigerant that is not appropriate, then there is a risk that the functions of the air conditioner will decline. Consequently, there is a need to determine whether the refrigerant circuit is filled with an appropriate amount of refrigerant. 
     Accordingly, among air conditioners that comprise a receiver, the interior of which can pool the refrigerant inside the refrigerant circuit, there exists an air conditioner that is provided with a liquid surface detecting means, which detects the liquid surface of the refrigerant pooled inside the receiver. With regard to this air conditioner, a refrigerant amount determining operation that determines the amount of refrigerant that has been filled in the refrigerant circuit by performing control that maintains the liquid surface inside the receiver at a constant level has been proposed (refer to Japanese Patent Application Publication No. 2006-292212). 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     Nevertheless, in an air conditioner that does not comprise the receiver, it is difficult to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant. In addition, even in an air conditioner that does comprise the receiver, if the air conditioner does not have a refrigerant amount determining operation function, it is still difficult to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant. 
     It is an object of the present invention to provide an air conditioner that can determine whether a refrigerant circuit is filled with the appropriate amount of refrigerant, even when a receiver is not provided. 
     Solution to Problem 
     An air conditioner according to a first aspect of the present invention comprises a compressor, a first heat exchanger, a high pressure piping, a second heat exchanger, a low pressure piping, a pressure reducing mechanism, a bypass passageway, a vessel, a first opening/closing mechanism, and a second opening/closing mechanism. The compressor compresses a refrigerant. The first heat exchanger is connected to a discharge port of the compressor and functions as a condenser. The high pressure piping extends from the first heat exchanger. The second heat exchanger is connected to the first heat exchanger via the high pressure piping and function as evaporators. The low pressure piping connects the second heat exchangers and the suction port of the compressor. The pressure reducing mechanism is provided to the high pressure piping. The bypass passageway diverts the refrigerant from the high pressure piping to the low pressure piping without passing through the second heat exchangers. The vessel is provided to the bypass passageway. The first opening/closing mechanism is provided to a first portion of the bypass passageway that connects the high pressure piping and the vessel. The second opening/closing mechanism is provided to a second portion of the bypass passageway that connects an upper part of the vessel and the low pressure piping. 
     In the air conditioner according to the first aspect of the present invention, the vessel, the first opening/closing mechanism, and the second opening/closing mechanism are provided to the bypass passageway. The vessel is capable of pooling the refrigerant. In addition, the first opening/closing mechanism is capable of blocking the refrigerant that flows from the high pressure piping into the vessel. Furthermore, the second opening/closing mechanism is capable of blocking the refrigerant that flows from the vessel to the low pressure piping. Consequently, a prescribed amount of the refrigerant can be pooled in the vessel by regulating the first opening/closing mechanism and the second opening/closing mechanism. 
     Thereby, it is possible to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant. 
     An air conditioner according to a second aspect of the present invention is the air conditioner according to the first aspect of the present invention, wherein the compressor, the first heat exchanger, the high pressure piping, the second heat exchangers, and the low pressure piping constitute a main refrigerant circuit. In addition, a piping whose diameter is smaller than that of the high pressure piping is used for the first portion and the second portion of the bypass passageway. 
     In the air conditioner according to a second aspect of the present invention, the diameters of the pipings of the first portion and the second portion of the bypass passageway are smaller than that of the high pressure piping. Consequently, it is possible to use an opening/closing mechanism wherein the first opening/closing mechanism and the second opening/closing mechanism provided to the bypass passageway are smaller than, for example, the case wherein the opening/closing mechanism is provided to the high pressure piping. 
     Thereby, in this air conditioner, it is possible to reduce the cost of the opening/closing mechanism. 
     An air conditioner according to a third aspect of the present invention is the air conditioner according to the second aspect of the present invention and further comprises a control unit, which controls an overfill determination. An overfill operation control comprises a first step, a second step, a third step, and a fourth step and controls the determination of whether the refrigerant is in an excessively filled state. 
     With the air conditioner according to a third aspect of the present invention, the control unit performs the first step, the second step, the third step, and the fourth step during the overfill determination control. In the first step, the control unit performs control that sets the first opening/closing mechanism and the second opening/closing mechanism to an open state. Accordingly, the refrigerant is recovered from the high pressure piping into the vessel. In the second step, the control unit performs control that detects that the liquid refrigerant has begun to flow from the vessel to the low pressure piping. In the third step, the control unit performs control that sets at least the second opening/closing mechanism to the closed state in accordance with the fact that the start of flow of the liquid refrigerant to the low pressure piping has been detected in the second step. In the fourth step, the control unit performs control that, after the detection of the start of flow of the liquid refrigerant to the low pressure piping in the second step, determines whether the amount of the refrigerant in the main refrigerant circuit is in the insufficient range or in the sufficient range. Thereby, in the fourth step, the control unit determines whether the main refrigerant circuit is overfilled with the refrigerant. 
     Thereby, it is possible to determine that the refrigerant circuit is overfilled with the refrigerant. 
     An air conditioner according to a fourth aspect of the present invention is the air conditioner according to the third aspect of the present invention, wherein the determination, in the fourth step, of whether the amount of the refrigerant in the main refrigerant circuit is in the insufficient range or the sufficient range is a determination of whether the refrigerant at an outlet of the first heat exchanger is in the vapor-liquid two-phase or the liquid phase. 
     In the air conditioner according to the fourth aspect of the present invention, the amount of refrigerant with which the main refrigerant circuit is filled is determined by the state of the refrigerant at the outlet of the first heat exchanger. Consequently, in this air conditioner, it is possible to easily determine whether the amount of refrigerant in the main refrigerant circuit is appropriate. 
     An air conditioner according to a fifth aspect of the present invention is the air conditioner according to the fourth aspect of the present invention and further comprises a first temperature sensor and a second temperature sensor. The first temperature sensor detects the temperature of the refrigerant on the upstream side of the pressure reducing mechanism. The second temperature sensor detects the temperature of the refrigerant on the downstream side of the pressure reducing mechanism. In addition, in the fourth step, the control unit determines whether the refrigerant at the outlet of the first heat exchanger is in the liquid phase or in the vapor-liquid two-phase state and, based on that determination, determines whether there is an overfilled state. 
     The air conditioner according to the fifth aspect of the present invention further comprises the first temperature sensor and the second temperature sensor. Consequently, it is possible to detect the temperature of the refrigerant on the upstream side and the downstream side of the pressure reducing mechanism. The control unit calculates the difference between the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor, and, if that difference is less than or equal to a first threshold value, then the control unit determines that the refrigerant at the outlet of the first heat exchanger is in the liquid phase. In addition, if that difference is greater than the first threshold value, then the control unit determines that the refrigerant at the outlet of the first heat exchanger is in the vapor-liquid two-phase state. If the refrigerant at the outlet of the first heat exchanger is in the liquid phase, then the control unit determines that the refrigerant is in an overfilled state; further, if the refrigerant at the outlet of the first heat exchanger is in the vapor-liquid two-phase state, then the control unit determines that the refrigerant is not in an overfilled state. 
     Thereby, it is possible to determine that the refrigerant circuit is overfilled with the refrigerant. 
     An air conditioner according to a sixth aspect of the present invention is the air conditioner according to the third aspect of the present invention, wherein the determination, in the fourth step, of whether the amount of the refrigerant in the main refrigerant circuit is in the insufficient region or the sufficient range is a determination of whether the degree of supercooling of the refrigerant at the outlet of the first heat exchanger is less than or equal to a second threshold value or greater than a second threshold value. Consequently, it is possible to determine the amount of refrigerant with which the main refrigerant circuit is filled based on the degree of supercooling on the outlet side of the first heat exchanger. 
     Thereby, it is possible to determine that the refrigerant circuit is overfilled with the refrigerant. 
     An air conditioner according to a seventh aspect of the present invention is the air conditioner according to the third through sixth aspects of the present invention, wherein the control unit monitors, in the second step, the difference between a discharge side refrigerant temperature of the compressor and a condensing temperature of the first heat exchanger. In addition, when the degree of descent per unit of time of the difference between the discharge side refrigerant temperature of the compressor and the condensing temperature of the first heat exchanger is greater than a third threshold value, the control unit determines that the liquid refrigerant has begun to flow from the vessel to the low pressure piping through the second portion of the bypass passageway. Consequently, it is possible to determine that the refrigerant is overflowing from the vessel. 
     An air conditioner according to an eighth aspect of the present invention is the air conditioner according to the first aspect of the present invention and further comprises a third opening/closing mechanism. The third opening/closing mechanism is provided to a third portion, which is separate from the second portion, of the bypass passageway. The third portion connects a lower part of the vessel and the low pressure piping and is provided with a bypass pressure reducing mechanism that has a pressure reducing function. 
     In the air conditioner according to the eighth aspect of the present invention, a third opening/closing mechanism is provided. In addition, a bypass pressure reducing mechanism is provided to the third portion, which is provided by the third opening/closing mechanism. Consequently, it is possible to depressurize the liquid refrigerant pooled in the vessel and guide to the low pressure piping. 
     Thereby, it is possible to regulate the amount of refrigerant flowing through the main refrigerant circuit. 
     An air conditioner according to a ninth aspect of the present invention is the air conditioner according to the eighth aspect of the present invention and further comprises a control unit, which performs refrigerant adjustment control in a normal operation. In addition, a main refrigerant circuit of this air conditioner comprises the compressor, the first heat exchanger, the high pressure piping, the second heat exchangers, and the low pressure piping. In the refrigerant adjustment control, when it is determined that an excessive amount of the refrigerant is flowing through the main refrigerant circuit, the control unit sets the first opening/closing mechanism and the second opening/closing mechanism to the open state and the third opening/closing mechanism to the closed state. In addition, when it is determined that an insufficient amount of the refrigerant is flowing through the main refrigerant circuit, the control unit sets the first opening/closing mechanism and the second opening/closing mechanism to the closed state and the third opening/closing mechanism to the open state. 
     The air conditioner according to the ninth aspect of the present invention further comprises a control unit, which performs refrigerant regulation control in the normal operation. When it is determined in the refrigerant adjustment control that an excessive amount of the refrigerant is flowing through the main refrigerant circuit, the control unit performs control such that the first opening/closing mechanism and the second opening/closing mechanism are set to the open state, the third opening/closing mechanism is set to the closed state, and a prescribed amount of the refrigerant is recovered in the vessel. In addition, when it is determined that an insufficient amount of the refrigerant is flowing through the main refrigerant circuit, the control unit sets the first opening/closing mechanism and the second opening/closing mechanism to the closed state, sets the third opening/closing mechanism to the open state, and discharges the refrigerant from the vessel to the low pressure piping. Consequently, it is possible to regulate the amount of refrigerant flowing through the main refrigerant circuit in accordance with the excess or insufficiency of the refrigerant flowing through the main refrigerant circuit. 
     Thereby, it is possible to stably maintain the functions of the air conditioner. 
     Advantageous Effects of Invention 
     With the air conditioner according to the first aspect of the present invention, it is possible to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant. 
     With the air conditioner according to the second aspect of the present invention, it is possible to reduce the cost of the opening/closing mechanisms. 
     With the air conditioner according to the third aspect of the present invention, it is possible to determine that the refrigerant circuit is overfilled with the refrigerant. 
     With the air conditioner according to the fourth aspect of the present invention, it is possible to easily determine whether the main refrigerant circuit is filled with the appropriate amount of refrigerant. 
     With the air conditioner according to the fifth aspect of the present invention, it is possible to determine that the refrigerant circuit is overfilled with the refrigerant. 
     With the air conditioner according to the sixth aspect of the present invention, it is possible to determine that the refrigerant circuit is overfilled with the refrigerant. 
     With the air conditioner according to the seventh aspect of the present invention, it is possible to determine that the refrigerant is overflowing from the vessel. 
     With the air conditioner according to the eighth aspect of the present invention, it is possible to regulate the amount of refrigerant flowing through the main refrigerant circuit. 
     With the air conditioner according to the ninth aspect of the present invention, it is possible to stably maintain the functions of the air conditioner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic refrigerant circuit diagram of an air conditioner according to an embodiment of the present invention. 
         FIG. 2  is a schematic longitudinal cross sectional view of a refrigerant adjustment vessel. 
         FIG. 3  is a control block diagram of the air conditioner according to the embodiment of the present invention. 
         FIG. 4  is a flow chart of a refrigerant amount determining operation in the air conditioner according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Configuration of Air Conditioner 
       FIG. 1  schematically shows a refrigerant circuit  10  of an air conditioner  100  according to one embodiment of the present invention. 
     The air conditioner  100  principally comprises: an outdoor unit  1 ; two indoor units  2   a ,  2   b , which are connected in parallel to the outdoor unit  1 ; and a liquid refrigerant connection piping  11  and a gas refrigerant connection piping  12 , which serve as refrigerant connection pipings that connect the outdoor unit  1  with the indoor units  2   a ,  2   b . Specifically, the liquid refrigerant connection piping  11  and the gas refrigerant connection piping  12  are connected to an outdoor side refrigerant piping  13  of the outdoor unit  1  and indoor side refrigerant pipings  14   a ,  14   b  of the indoor units  2   a ,  2   b , respectively. Namely, the refrigerant circuit  10  of the air conditioner  100  is configured by connecting the outdoor side refrigerant piping  13 , the indoor side refrigerant pipings  14   a ,  14   b , the liquid refrigerant connection piping  11 , and the gas refrigerant connection piping  12 . In addition, the outdoor side refrigerant piping  13  comprises an outdoor side main refrigerant piping  18   a  and a bypass piping  18   b . Furthermore, in the present embodiment, a circuit that is configured by connecting the indoor side refrigerant pipings  14   a ,  14   b , the outdoor side main refrigerant piping  18   a , the liquid refrigerant connection piping  11 , and the gas refrigerant connection piping  12 , each of which are part of the refrigerant circuit  10 , is called the main refrigerant circuit  30 . In addition, in the main refrigerant circuit  30 , the piping wherethrough the refrigerant flows from a heat exchanger that functions as a condenser toward a heat exchanger that functions as an evaporator is called a liquid refrigerant piping  15 , and a piping wherethrough the refrigerant flows from the heat exchanger that functions as an evaporator toward the heat exchanger that functions as a condenser is called a gas refrigerant piping  16 . Below, in the various pieces of equipment that are provided to and disposed in the main refrigerant circuit  30  (discussed below), the side that is connected to the liquid refrigerant piping  15  is called the liquid side, and the side that is connected to the gas refrigerant piping  16  is called the gas side. In addition, the liquid refrigerant connection piping  11  is included in the liquid refrigerant piping  15 , and the gas refrigerant connection piping  12  is included in the gas refrigerant piping  16 . 
     (Indoor Unit) 
     The indoor units  2   a ,  2   b  are installed by, for example, embedding them in or suspending them from the indoor ceiling of a building or the like, or by attaching them to an indoor wall surface. As discussed above, the indoor units  2   a ,  2   b  comprise the indoor side refrigerant pipings  14   a ,  14   b , which constitute part of the main refrigerant circuit  30 . The indoor side refrigerant pipings  14   a ,  14   b  principally comprise indoor expansion valves  9   a ,  9   b  and indoor heat exchangers  4   a ,  4   b , each of which is connected via a refrigerant piping, as shown in  FIG. 1 . 
     The indoor expansion valves  9   a ,  9   b  are motor operated expansion valves, which, to regulate the flow volume of the refrigerant that flows inside the indoor side refrigerant pipings  14   a ,  14   b , are connected to the liquid sides of the indoor heat exchangers  4   a ,  4   b.    
     The indoor heat exchangers  4   a ,  4   b  are cross fin type fin and tube heat exchangers, which comprise heat transfer pipes and numerous fins. In addition, the indoor heat exchangers  4   a ,  4   b  function as refrigerant evaporators during a cooling operation to cool the indoor air and function as refrigerant condensers during a heating operation to heat the indoor air. 
     In addition, the indoor units  2   a ,  2   b  are provided with indoor heat exchanger liquid side temperature sensors  35   a ,  35   b , indoor heat exchanger gas side temperature sensors  37   a ,  37   b , and indoor heat exchanger temperature sensors  36   a ,  36   b . The indoor heat exchanger liquid side temperature sensors  35   a ,  35   b  are provided on the liquid sides of the indoor heat exchangers  4   a ,  4   b  and detect the temperature of the refrigerant in both the liquid state and the vapor-liquid two-phase state. The indoor heat exchanger gas side temperature sensors  37   a ,  37   b  are provided on the gas sides of the indoor heat exchangers  4   a ,  4   b  and detect the temperature of the refrigerant in both the gas state and the vapor-liquid two-phase state. In addition, the indoor heat exchanger temperature sensors  36   a ,  36   b  are provided to the indoor heat exchangers  4   a ,  4   b  and detect the temperature of the refrigerant that flows therein. In the present embodiment, the indoor heat exchanger liquid side temperature sensors  35   a ,  35   b , the indoor heat exchanger gas side temperature sensors  37   a ,  37   b , and the indoor heat exchanger temperature sensors  36   a ,  36   b  are composed of thermistors. 
     (Outdoor Unit) 
     The outdoor unit  1  is installed on, for example, the rooftop of a building and the like; furthermore, as discussed above, the outdoor unit  1  comprises the outdoor side main refrigerant piping  18   a  and the bypass piping  18   b , which constitute part of the refrigerant circuit  10 . 
     The outdoor side main refrigerant piping  18   a  principally comprises a compressor  5 , a four-way switching valve  6 , an outdoor heat exchanger  3 , an outdoor expansion valve  8 , a liquid side shutoff valve  50 , and a gas side shutoff valve  51 , each of which is connected via refrigerant pipings, as shown in  FIG. 1 . The outdoor side main refrigerant piping  18   a  comprises an outdoor side liquid refrigerant piping  15   a , which is part of the liquid refrigerant piping  15 , and an outdoor side gas refrigerant piping  16   a , which is part of the gas refrigerant piping  16 . The outdoor side liquid refrigerant piping  15   a  is the piping which connects the liquid side of the outdoor heat exchanger  3  and the liquid side shutoff valve  50  and comprises a first outdoor side liquid refrigerant piping  15   b  is the piping which and a second outdoor side liquid refrigerant piping  15   c  is the piping which. The first outdoor side liquid refrigerant piping  15   b  connects the liquid side of the outdoor heat exchanger  3  and the outdoor expansion valve  8 . The second outdoor side liquid refrigerant piping  15   c  connects the outdoor expansion valve  8  and the liquid side shutoff valve  50 . In addition, the outdoor side gas refrigerant piping  16   a  comprises a first outdoor side gas refrigerant piping  16   b  is the piping which, a second outdoor side gas refrigerant piping  16   c  is the piping which, a third outdoor side gas refrigerant piping  16   d  is the piping which, and a fourth outdoor side gas refrigerant piping  16   e  is the piping which and connects the gas side shutoff valve  51  and the gas side of the outdoor heat exchanger  3 . The first outdoor side gas refrigerant piping  16   b  connects the gas side shutoff valve  51  and the four-way switching valve  6 . The second outdoor side gas refrigerant piping  16   c  connects the four-way switching valve  6  and a suction side of the compressor  5 . The third outdoor side gas refrigerant piping  16   d  connects a discharge side of the compressor  5  and the four-way switching valve  6 . The fourth outdoor side gas refrigerant piping  16   e  connects the four-way switching valve  6  and the gas side of the outdoor heat exchanger  3 . 
     As shown in  FIG. 1 , the bypass piping  18   b  comprises a refrigerant inflow piping  17 , a refrigerant outflow piping  19 , and a refrigerant adjustment unit  20 . One end of the refrigerant inflow piping  17  is connected to the second outdoor side liquid refrigerant piping  15   c , and the other end of the refrigerant inflow piping  17  is connected to a refrigerant adjustment vessel  21  of the refrigerant adjustment unit  20 . In addition, one end of the refrigerant outflow piping  19  is connected to the refrigerant adjustment vessel  21 , and the other end of the refrigerant outflow piping  19  is connected to the second outdoor side gas refrigerant piping  16   c.    
     The compressor  5  is an apparatus that compresses the low pressure gas refrigerant sucked in from the suction side and discharges this pressurized high pressure gas refrigerant to the discharge side. In addition, the compressor  5  is capable of varying its operating capacity and is driven by a motor that is controlled by an inverter. 
     The four-way switching valve  6  is for switching the direction of the refrigerant&#39;s flow; during the cooling operation, refrigerant filling operation, and refrigerant amount determining operation, the four-way switching valve  6  connects the discharge side of the compressor  5  and the gas side of the outdoor heat exchanger  3 , as well as the suction side of the compressor  5  and the gas refrigerant connection piping  12  (refer to the solid lines of the four-way switching valve  6  in  FIG. 1 ). Accordingly, during the cooling operation, refrigerant filling operation, and refrigerant amount determining operation, the outdoor heat exchanger  3  functions as a condenser of the refrigerant compressed in the compressor  5 , and the indoor heat exchangers  4   a ,  4   b  function as evaporators of the refrigerant condensed in the outdoor heat exchanger  3 . In addition, during the heating operation, the four-way switching valve  6  connects the discharge side of the compressor  5  and the gas refrigerant connection piping  12  and connects the suction side of the compressor  5  and the gas side of the outdoor heat exchanger  3  (refer to the broken lines of the four-way switching valve  6  in  FIG. 1 ). Accordingly, during the heating operation, the indoor heat exchangers  4   a ,  4   b  function as condensers of the refrigerant compressed in the compressor  5 , and the outdoor heat exchanger  3  functions as an evaporator of the refrigerant condensed in the indoor heat exchangers  4   a ,  4   b.    
     The outdoor heat exchanger  3  is a cross fin type fin and tube heat exchanger that comprises a heat transfer pipe and a plurality of fins; during the cooling operation, the outdoor heat exchanger  3  functions as a condenser of the refrigerant; during the heating operation, the outdoor heat exchanger  3  functions as an evaporator of the refrigerant. The gas side of the outdoor heat exchanger  3  is connected to the four-way switching valve  6 , and the liquid side of the outdoor heat exchanger  3  is connected to the outdoor expansion valve  8 . 
     In addition, the outdoor unit  1  comprises an outdoor fan  7 , which sucks the outdoor air into the outdoor unit  1 , supplies it to the outdoor heat exchanger  3 , and then discharges it to the outdoor space. The outdoor fan  7  is capable of varying the flow volume of the air supplied to the outdoor heat exchanger  3 ; in the present embodiment, the outdoor fan  7  is a propeller fan that is driven by a motor, which consists of a DC fan motor. 
     The outdoor expansion valve  8  is a motor operated expansion valve for, for example, regulating the flow volume of the refrigerant that flows inside the outdoor side refrigerant piping  13  and is connected to the liquid side of the outdoor heat exchanger  3 . 
     The refrigerant adjustment unit  20  is a vertical cylinder and, as discussed above, is connected to the main refrigerant circuit  30  via the bypass piping  18   b . The refrigerant adjustment unit  20  is capable of pooling the refrigerant that flows through the main refrigerant circuit  30  to the refrigerant adjustment vessel  21  of the refrigerant adjustment unit  20 . Furthermore, the structure of the refrigerant adjustment unit  20  is discussed below. 
     The liquid side shutoff valve  50  is provided with connection ports for connecting to the liquid refrigerant connection piping  11  and the outdoor unit  1 . In addition, the gas side shutoff valve  51  is provided with connection ports for connecting to the gas refrigerant connection piping  12  and the outdoor unit  1 . The liquid side shutoff valve  50  is connected to the outdoor expansion valve  8 . The gas side shutoff valve  51  is connected to the four-way switching valve  6 . 
     In addition, the outdoor unit  1  is provided with a discharge side temperature sensor  31 , an outdoor heat exchanger temperature sensor  32 , an expansion valve inlet side temperature sensor  33 , and an expansion valve outlet side temperature sensor  34 . The discharge side temperature sensor  31  is provided to the discharge side of the compressor  5 . The compressor  5  detects a discharge temperature Td. The outdoor heat exchanger temperature sensor  32  is provided to the outdoor heat exchanger  3  and detects the temperature of the refrigerant that flows therein. The expansion valve inlet side temperature sensor  33  is provided to the first outdoor side liquid refrigerant piping  15   b  and detects the temperature of the refrigerant that flows therethrough. The expansion valve outlet side temperature sensor  34  is provided to the second outdoor side liquid refrigerant piping  15   c  and detects the temperature of the refrigerant that flows therethrough. Furthermore, in the present embodiment, the discharge side temperature sensor  31 , the outdoor heat exchanger temperature sensor  32 , the expansion valve inlet side temperature sensor  33 , and the expansion valve outlet side temperature sensor  34  are composed of thermistors. 
     (Structure of Refrigerant Adjustment Unit) 
     The refrigerant adjustment unit  20  is connected to the main refrigerant circuit  30  via the refrigerant inflow piping  17  and the refrigerant outflow piping  19 , which constitute the bypass piping  18   b , as discussed above. In addition, as shown in  FIG. 1  and  FIG. 2 , the refrigerant adjustment unit  20  principally comprises: the refrigerant adjustment vessel  21 , which is capable of pooling the refrigerant; a liquid refrigerant inlet pipe  27 , which is part of the refrigerant inflow piping  17 ; and a liquid refrigerant outlet pipe  29  and an overflow pipe  28 , which are parts of the refrigerant outflow piping  19 . 
     The refrigerant adjustment vessel  21  is a vertical cylinder that is capable of pooling a prescribed amount of the refrigerant. 
     A liquid refrigerant inlet pipe end part  27   a  of the liquid refrigerant inlet pipe  27  has an opening wherethrough the liquid refrigerant that flows through the second outdoor side liquid refrigerant piping  15   c  can flow into the refrigerant adjustment vessel  21 . In addition, as shown in  FIG. 2 , the liquid refrigerant inlet pipe  27  is provided to an upper part of the refrigerant adjustment vessel  21  such that the liquid refrigerant can flow into the refrigerant adjustment vessel  21  from a position that is higher than a position L 1  of the liquid surface of the liquid refrigerant pooled in the refrigerant adjustment vessel  21 . Furthermore, as shown in  FIG. 1 , the liquid refrigerant inlet pipe  27  comprises a first solenoid valve  22  and a check valve  23 . In the liquid refrigerant inlet pipe  27 , the first solenoid valve  22  and the check valve  23  are disposed in series with respect to the flow of the refrigerant. In addition, the check valve  23  is attached such that the refrigerant is only permitted to flow from the second outdoor side liquid refrigerant piping  15   c  toward the refrigerant adjustment vessel  21 . Furthermore, the first solenoid valve  22  is provided on the upstream side of the check valve  23 . 
     A liquid refrigerant outlet pipe end part  29   a  of the liquid refrigerant outlet pipe  29  has an opening wherethrough the refrigerant can flow out from a lower part of the refrigerant adjustment vessel  21  to the second outdoor side gas refrigerant piping  16   c . In addition, as shown in  FIG. 2 , the liquid refrigerant outlet pipe end part  29   a  of the liquid refrigerant outlet pipe  29  is disposed in the vicinity of a bottom part of the refrigerant adjustment vessel  21 . Furthermore, as shown in  FIG. 1  the liquid refrigerant outlet pipe  29  comprises a third solenoid valve  25  and a capillary tube  26 . The capillary tube  26  reduces the pressure of the refrigerant that flows through the liquid refrigerant outlet pipe  29 . Furthermore, in the liquid refrigerant outlet pipe  29 , the third solenoid valve  25  is provided on the upstream side of the capillary tube  26 . 
     One end of the overflow pipe  28  is connected to an upper part of the refrigerant adjustment vessel  21 , and the other end of the overflow pipe  28  is connected to the liquid refrigerant outlet pipe  29 . Consequently, as shown in  FIG. 2 , the overflow pipe  28  flows the liquid refrigerant out of the refrigerant adjustment vessel  21  only when the position L 1  of the liquid surface of the liquid refrigerant pooled inside the refrigerant adjustment vessel  21  reaches a position L 2  at the upper part of the refrigerant adjustment vessel  21 . In addition, a connecting part between the overflow pipe  28  and the liquid refrigerant outlet pipe  29  is disposed inside the refrigerant adjustment unit  20  and positioned on the downstream side of the capillary tube  26 , which is provided to and disposed in the liquid refrigerant outlet pipe  29 . Consequently, the overflow pipe  28  can guide the liquid refrigerant from the refrigerant adjustment vessel  21  to the liquid refrigerant outlet pipe  29  only when the position L 1  of the liquid surface of the liquid refrigerant pooled inside the refrigerant adjustment vessel  21  reaches the position L 2  of the upper part of the refrigerant adjustment vessel  21 . In addition, as shown in  FIG. 1 , the overflow pipe  28  comprises a second solenoid valve  24 . 
     Furthermore, the pipe diameters of the refrigerant pipings adapted to the liquid refrigerant inlet pipe  27 , the liquid refrigerant outlet pipe  29 , and the overflow pipe  28  are all equal to one another and smaller than the pipe diameter of the refrigerant piping adapted to the main refrigerant circuit  30 . 
     (Control Unit) 
     As shown in  FIG. 3 , the air conditioner  100  comprises a control unit  60 , which operates and controls each piece of equipment that constitutes the air conditioner  100 . The control unit  60  comprises an indoor side control unit  61  and an outdoor side control unit  62  and performs not only normal operations, which include the cooling operation and the heating operation, but also a refrigerant filling operation and a refrigerant amount determining operation. 
     The indoor side control unit  61  controls the operation of all of the parts that constitute the indoor units  2   a ,  2   b . The indoor side control unit  61  comprises, for example, a microcomputer, which is provided to control the indoor units  2   a ,  2   b , and a memory and is capable of exchanging control signals and the like with the remote controls for separately operating the indoor units  2   a ,  2   b . In addition, the indoor side control unit  61  is connected to the indoor heat exchanger liquid side temperature sensors  35   a ,  35   b , the indoor heat exchanger gas side temperature sensors  37   a ,  37   b , and the indoor heat exchanger temperature sensors  36   a ,  36   b . Consequently, based on the temperatures of the refrigerant detected by the indoor heat exchanger liquid side temperature sensors  35   a ,  35   b , the indoor heat exchanger gas side temperature sensors  37   a ,  37   b , and the indoor heat exchanger temperature sensors  36   a ,  36   b , the indoor side control unit  61  calculates either degrees of overheating when the indoor heat exchangers  4   a ,  4   b  function as evaporators or degrees of supercooling when the indoor heat exchangers  4   a ,  4   b  function as condensers. Furthermore, the indoor side control unit  61  regulates the opening degrees of the indoor expansion valves  9   a ,  9   b  based on the calculated degrees of overheating or degrees of supercooling. 
     The outdoor side control unit  62  controls the operation of all of the parts that constitute the outdoor unit  1 . The outdoor side control unit  62  comprises, for example, a microcomputer, which is provided to control the outdoor unit  1 , and an inverter circuit, which controls the memory and the motor, and is capable of exchanging control signals and the like with the indoor side control unit  61 . In addition, the outdoor side control unit  62  is connected to the discharge side temperature sensor  31  and the outdoor heat exchanger temperature sensor  32  and performs an overflow determination (discussed below) by controlling the opening and closing of the first solenoid valve  22  and the second solenoid valve  24  based on the temperatures of the refrigerant detected by the discharge side temperature sensor  31  and the outdoor heat exchanger temperature sensor  32 . Furthermore, the outdoor side control unit  62  is connected to the expansion valve inlet side temperature sensor  33  and the expansion valve outlet side temperature sensor  34  and performs an overfill determination (discussed below) based on the temperatures of the refrigerant detected by the expansion valve inlet side temperature sensor  33  and the expansion valve outlet side temperature sensor  34 . 
     Furthermore, if a surplus of refrigerant is detected in the main refrigerant circuit  30  during the cooling operation or the heating operation, the outdoor side control unit  62  performs control that switches the first solenoid valve  22  to the open state such that the refrigerant is guided from the main refrigerant circuit  30  to the refrigerant adjustment unit  20 . In addition, if an insufficient amount of the refrigerant is detected inside the main refrigerant circuit  30  during the cooling operation or the heating operation, the outdoor side control unit  62  performs control that switches the third solenoid valve  25  to the open state such that the refrigerant is guided from the refrigerant adjustment unit  20  to the main refrigerant circuit  30 . Furthermore, an excess or deficient amount of the refrigerant in the main refrigerant circuit  30  is determined based on the degrees of overheating and the degrees of supercooling in the indoor heat exchangers  4   a ,  4   b  calculated by the indoor side control unit  61 . 
     In addition, the control unit  60  performs an operation that switches the cooling operation and the heating operation via the four-way switching valve  6  and controls each piece of equipment, such as the compressor  5  of the outdoor unit  1 , in accordance with the operating loads of the indoor units  2   a ,  2   b . Furthermore, a warning display unit  63 , which comprises an LED and the like for reporting that the refrigerant is in the overfilled state in a refrigerant amount determining operation mode (discussed below), is connected to the control unit  60 . 
     &lt;Operation of Air Conditioner&gt; 
     The following text explains the operation of the air conditioner  100  of the present embodiment. 
     The operation modes of the air conditioner  100  of the present embodiment include: a normal operation mode, which controls each piece of equipment of the outdoor unit  1  and the indoor units  2   a ,  2   b  in accordance with the operating loads of the indoor units  2   a ,  2   b ; a refrigerant filling operation mode, which is performed after the air conditioner  100  has been installed; and the refrigerant amount determining operation mode, which determines whether the main refrigerant circuit  30  is filled with the appropriate amount of refrigerant. Furthermore, the normal operation mode principally includes the cooling operation and the heating operation. 
     The following text explains the operation performed in each operation mode of the air conditioner  100 . 
     (Normal Operation Mode) 
     First, the cooling operation in the normal operation mode will be explained, referencing  FIG. 1 . 
     During the cooling operation, the four-way switching valve  6  is in the state indicated by the solid lines in the figure, namely, the state wherein the discharge side of the compressor  5  is connected to the gas side of the outdoor heat exchanger  3 , and the suction side of the compressor  5  is connected to the gas side of the indoor heat exchangers  4   a ,  4   b . In addition, the outdoor expansion valve  8  is set to the open state and the opening degrees of the indoor expansion valves  9   a ,  9   b  are regulated such that the degrees of overheating of the refrigerant on the gas sides of the indoor heat exchangers  4   a ,  4   b  reach prescribed values. Furthermore, in the present embodiment, the degrees of overheating of the refrigerant on the gas sides of the indoor heat exchangers  4   a ,  4   b  are detected by subtracting the refrigerant temperature values detected by the indoor heat exchanger liquid side temperature sensors  35   a ,  35   b  from the refrigerant temperature values detected by the indoor heat exchanger gas side temperature sensors  37   a ,  37   b . In addition, the first solenoid valve  22 , the second solenoid valve  24 , and the third solenoid valve  25  are set to the closed state. 
     If the compressor  5  is activated with the refrigerant circuit  10  in this state, then the low pressure gas refrigerant is sucked into the compressor  5  and compressed and thereby turns into high pressure gas refrigerant. Subsequently, the high pressure gas refrigerant transits the four-way switching valve  6  and is fed to the outdoor heat exchanger  3 . The high pressure gas refrigerant fed to the outdoor heat exchanger  3  exchanges heat with the outdoor air supplied by the outdoor fan  7 , condenses, and thereby turns into high pressure liquid refrigerant. 
     Furthermore, the high pressure liquid refrigerant transits the liquid refrigerant connection piping  11  and is fed to the indoor units  2   a ,  2   b . The pressure of the high pressure liquid refrigerant fed to the indoor units  2   a ,  2   b  is reduced by the indoor expansion valves  9   a ,  9   b , and thereby the high pressure liquid refrigerant turns into low pressure refrigerant in the vapor-liquid two-phase state, is fed to the indoor heat exchangers  4   a ,  4   b , exchanges heat with the indoor air via the indoor heat exchangers  4   a ,  4   b , evaporates, and turns into low pressure gas refrigerant. Here, the indoor expansion valves  9   a ,  9   b  control the amounts of flow of the refrigerant that flows in the indoor heat exchangers  4   a ,  4   b  such that the degrees of overheating on the gas sides of the indoor heat exchangers  4   a ,  4   b  reach prescribed values. This low pressure gas refrigerant transits the gas refrigerant connection piping  12 , is fed to the outdoor unit  1 , transits the gas side shutoff valve  51  and the four-way switching valve  6 , and is once again sucked into the compressor  5 . 
     Furthermore, in accordance with the operating loads of the indoor units  2   a ,  2   b , there may be a surplus of refrigerant inside the main refrigerant circuit  30  if, for example, the operating load of one of the indoor units  2   a ,  2   b  is small or stopped or if the operating loads of both of the indoor units  2   a ,  2   b  are small. If the outdoor side control unit  62  determines that such a surplus refrigerant state has arisen, then the outdoor side control unit  62  sets the first solenoid valve  22  to the open state. Consequently, some of the refrigerant that flows through the main refrigerant circuit  30  is fed as surplus refrigerant to the refrigerant adjustment vessel  21 , wherein it pools temporarily. In addition, a state of insufficient refrigerant may arise in the main refrigerant circuit  30  if, for example, the operating loads of the indoor units  2   a ,  2   b  are large. Thus, if the outdoor side control unit  62  detects an insufficient refrigerant state, then the outdoor side control unit  62  sets the third solenoid valve  25  to the open state. Consequently, the pressure of the liquid refrigerant pooled in the refrigerant adjustment vessel  21  decreases when it passes through the capillary tube  26 ; that liquid refrigerant then turns into gas refrigerant, merges with the gas refrigerant that flows through the second outdoor side gas refrigerant piping  16   c , and is sucked into the compressor  5 . 
     The following text explains the heating operation in the normal operation mode. 
     During the heating operation, the four-way switching valve  6  is in the state indicated by the broken lines in  FIG. 1 , namely, the state wherein the discharge side of the compressor  5  is connected to the gas side of the indoor side heat exchangers  4   a ,  4   b , and the suction side of the compressor  5  is connected to the gas side of the outdoor heat exchanger  3 . In addition, the outdoor expansion valve  8  is set to the open state and the opening degrees of the indoor expansion valves  9   a ,  9   b  are regulated such that the degrees of supercooling of the refrigerant on the liquid sides of the indoor heat exchangers  4   a ,  4   b  reach prescribed values. Furthermore, in the present embodiment, the degrees of supercooling of the refrigerant on the liquid sides of the indoor heat exchangers  4   a ,  4   b  are detected by subtracting the refrigerant temperatures that the indoor heat exchanger temperature sensors  36   a ,  36   b  detect—that is, the temperatures of the refrigerant that flows inside the indoor heat exchanger  4   a ,  4   b —from the refrigerant temperature values that the indoor heat exchanger liquid side temperature sensors  35   a ,  35   b  detect. In addition, the first solenoid valve  22 , the second solenoid valve  24 , and the third solenoid valve  25  are set to the closed state. 
     If the compressor  5  is activated with the refrigerant circuit  10  in this state, the low-pressure gas refrigerant is sucked into and compressed by the compressor  5 , turns into a high-pressure gas refrigerant, and is then fed to the indoor units  2   a ,  2   b  via the four-way switching valve  6  and the gas refrigerant connection piping  12 . 
     Furthermore, the high pressure gas refrigerant fed to the indoor units  2   a ,  2   b  exchanges heat with the indoor air in the indoor heat exchangers  4   a ,  4   b , is condensed, and turns into high pressure liquid refrigerant, after which its pressure is reduced by the indoor expansion valves  9   a ,  9   b ; thereby, that liquid refrigerant turns into vapor-liquid two-phase low pressure refrigerant. Here, the indoor expansion valves  9   a ,  9   b  control the amounts of flow of the refrigerant that flows inside the indoor heat exchanger  4   a ,  4   b  such that the degrees of supercooling on the liquid sides of the indoor heat exchangers  4   a ,  4   b  reach prescribed values. This low pressure refrigerant in the vapor-liquid two-phase state transits the liquid refrigerant connection piping  11 , is fed to the outdoor unit  1 , transits the outdoor expansion valve  8 , and flows into the outdoor heat exchanger  3 . Furthermore, the vapor-liquid two-phase low pressure refrigerant that flows into the outdoor heat exchanger  3  exchanges heat with the outdoor air supplied by the outdoor fan  7 , is condensed, turns into low pressure gas refrigerant, transits the four-way switching valve  6 , and is once again sucked into the compressor  5 . 
     Furthermore, as is the case during the cooling operation, in accordance with the operating loads of the indoor units  2   a ,  2   b , the refrigerant, for example, temporarily flows from the main refrigerant circuit  30  into the refrigerant adjustment vessel  21  and pools therein, or flows from the refrigerant adjustment vessel  21  to the main refrigerant circuit  30 , thereby supplementing the main refrigerant circuit  30 . 
     Thus, if the normal operation, including the cooling operation and the heating operation, is performed in the air conditioner  100 , then amounts of refrigerant flow to the indoor heat exchangers  4   a ,  4   b  in accordance with the operating loads demanded by the air conditioned spaces wherein the indoor units  2   a ,  2   b  are installed. 
     (Refrigerant Amount Determining Operation Mode) 
     Next, the refrigerant amount determining operation mode will be explained, referencing  FIG. 1 . Furthermore, the refrigerant amount determining operation, which is performed in the state wherein the main refrigerant circuit  30  is filled with the refrigerant, determines whether the main refrigerant circuit  30  is filled with the appropriate amount of refrigerant or is overfilled. The present embodiment explains an exemplary case wherein, when the indoor units  2   a ,  2   b  and the outdoor unit  1  are installed onsite and the main refrigerant circuit  30  is manually filled with the refrigerant, it is determined whether the main refrigerant circuit  30  is filled with an appropriate amount of the refrigerant. 
     After the refrigerant filling operation is complete, the refrigerant amount determining operation (refer to  FIG. 4 ) is performed to determine whether the main refrigerant circuit  30  is filled with the appropriate amount of refrigerant. When a refrigerant amount determining operation start instruction is output, the four-way switching valve  6  in the outdoor unit is set to the state indicated by the solid lines in  FIG. 1 , the outdoor expansion valve  8  and the indoor expansion valves  9   a ,  9   b  are set to the open state, and the first solenoid valve  22  and the second solenoid valve  24  are set to the open state (i.e., step S 1 ). The compressor  5  is activated with the refrigerant circuit  10  in this state, and thereby the cooling operation is forcibly performed. Consequently, some of the liquid refrigerant filled in the main refrigerant circuit  30  is fed to the refrigerant adjustment vessel  21  via the outdoor side liquid refrigerant piping  15   a , and thereby this liquid refrigerant pools inside the refrigerant adjustment vessel  21 . When the first solenoid valve  22  and the second solenoid valve  24  are set to the open state, it is determined whether the liquid refrigerant that pools inside the refrigerant adjustment vessel  21  is overflowing (i.e., step S 2 ). An overflow of the liquid refrigerant from the refrigerant adjustment vessel  21  occurs when the position L 1  of the liquid surface of the liquid refrigerant in the refrigerant adjustment vessel  21  reaches the position L 2  of the refrigerant adjustment vessel  21 , whereupon the liquid refrigerant flows toward the suction side of the compressor  5  via the overflow pipe  28  and the refrigerant outflow piping  19 . If the indoor side control unit  61  determines that there is an overflow from the refrigerant adjustment vessel  21 , then the outdoor side control unit  62  sets the first solenoid valve  22  and the second solenoid valve  24  to the closed state (i.e., step S 3 ). Thereby, the liquid refrigerant can no longer flow from the refrigerant adjustment vessel  21  to the second outdoor side gas refrigerant piping  16   c . Furthermore, the first solenoid valve  22  and the second solenoid valve  24  are set to the open state until the outdoor side control unit  62  detects an overflow. 
     Furthermore, in the state wherein an overflow has been detected, an overfill determination is made with respect to the amount of refrigerant in the main refrigerant circuit  30  (i.e., step S 4 ). The outdoor side control unit  62  makes an overfill determination with respect to the amount of refrigerant in the main refrigerant circuit  30  based on the state of the refrigerant in the first outdoor side liquid refrigerant piping  15   b  (i.e., step S 5 ). If it is determined that the refrigerant in the first outdoor side liquid refrigerant piping  15   b  is in the vapor-liquid two-phase state, then it is determined that the main refrigerant circuit  30  is not overfilled with the refrigerant, and the refrigerant amount determining operation is complete. In addition, if it is determined that the refrigerant in the first outdoor side liquid refrigerant piping  15   b  is in the liquid phase state, then a warning that reports that the main refrigerant circuit  30  is overfilled with the refrigerant is displayed on a warning display unit (i.e., step S 6 ). 
     In so doing, it is possible to detect in this air conditioner  100  whether the main refrigerant circuit  30  is overfilled with the refrigerant. 
     Next, the overflow determination and the overfill determination in the refrigerant amount determining operation will be discussed in detail. 
     (A) Overflow Determination 
     The overflow determination is made during the refrigerant amount determining operation. In addition, the overflow determination determines whether the liquid refrigerant is flowing out of the refrigerant adjustment vessel  21  to the suction side of the compressor  5 . Furthermore, in the refrigerant amount determining operation, the outdoor heat exchanger  3  functions as a condenser. Consequently, the temperature of the refrigerant detected by the outdoor heat exchanger temperature sensor  32  is designated as the refrigerant condensing temperature. 
     If the refrigerant in the liquid state is compressed, then a discharge temperature, which is the temperature of the refrigerant discharged from the compressor  5 , is lower than the discharge temperature when the refrigerant is in the gas state is compressed. Consequently, the vapor-liquid two-phase refrigerant, which is mixed with liquid refrigerant, is sucked into the compressor  5  and compressed, and therefore the difference between the discharge temperature and the condensing temperature at a prescribed time becomes small. Accordingly, if the position L 1  of the liquid surface of the refrigerant in the refrigerant adjustment vessel  21  reaches the position L 2  of the upper part of the refrigerant adjustment vessel  21 , then the liquid refrigerant flows out of the refrigerant adjustment vessel  21  to the second outdoor side gas refrigerant piping  16   c  via the overflow pipe  28  and the refrigerant outflow piping  19 . Furthermore, the liquid refrigerant that flows out merges with the gas refrigerant that flows through the second outdoor side gas refrigerant piping  16   c , and that liquid refrigerant turns into vapor-liquid two-phase refrigerant. This vapor-liquid two-phase refrigerant is sucked into and compressed by the compressor  5 , and therefore the difference between the discharge temperature of the compressor  5  and the condensing temperature at the prescribed time becomes small. Thereby, it is determined that the liquid refrigerant is overflowing from the refrigerant adjustment vessel  21 . 
     (B) Overfill Determination 
     Like the overflow determination, the overfill determination is made after it is determined that the liquid refrigerant is overflowing from the refrigerant adjustment vessel  21  to the second outdoor side gas refrigerant piping  16   c  during the refrigerant amount determination operation. 
     The overfill determination determines whether the refrigerant in the first outdoor side liquid refrigerant piping  15   b  is in the vapor-liquid two-phase state or the liquid phase state, and thereby determines whether the main refrigerant circuit  30  is overfilled with the refrigerant. 
     If the difference between the refrigerant temperature detected by the expansion valve inlet side temperature sensor  33  and the refrigerant temperature detected by the expansion valve outlet side temperature sensor  34  is greater than the prescribed value, then it is determined that the refrigerant flowing through the first outdoor side liquid refrigerant piping  15   b  is in the vapor-liquid two-phase state. In addition, if the difference between the refrigerant temperature detected by the expansion valve inlet side temperature sensor  33  and the refrigerant temperature detected by the expansion valve outlet side temperature sensor  34  is less than the prescribed value, then it is determined that the refrigerant flowing through the first outdoor side liquid refrigerant piping  15   b  is in the liquid phase. 
     Next, it is determined whether the main refrigerant circuit  30  is overfilled with the refrigerant. As discussed above, this determination is made in the state wherein a prescribed amount of the refrigerant filled in the main refrigerant circuit  30  pools inside the refrigerant adjustment vessel  21 . Consequently, if the main refrigerant circuit  30  is filled with an appropriate amount of the refrigerant, then the refrigerant in the main refrigerant circuit  30  is insufficient. Accordingly, if it is determined that the refrigerant flowing through the first outdoor side liquid refrigerant piping  15   b  is in the vapor-liquid two-phase state, then it is determined that the main refrigerant circuit  30  is overfilled with the refrigerant. In addition, if it is determined that the refrigerant flowing through the first outdoor side liquid refrigerant piping  15   b  is in the liquid phase state, then it is determined that the main refrigerant circuit  30  is overfilled with the refrigerant, namely, that the amount of the refrigerant exceeds the appropriate amount. 
     &lt;Features&gt; 
     (1) 
     In the conventional art, among air conditioners that comprise a receiver, the interior of which can pool the refrigerant inside the refrigerant circuit, there exists an air conditioner that is provided with a liquid surface detecting means, which detects the liquid surface of the refrigerant pooled inside the receiver. With regard to this air conditioner, a refrigerant amount determining operation that determines the amount of refrigerant that has been filled in the refrigerant circuit by performing control that maintains the liquid surface inside the receiver at a constant level has been proposed. 
     In an air conditioner that does not comprise the receiver, it is difficult to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant. In addition, even in an air conditioner that does comprise the receiver, if the air conditioner does not have a refrigerant amount determining operation function, it is still difficult to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant. 
     In contrast, the abovementioned embodiment comprises the refrigerant adjustment vessel  21 , the first solenoid valve  22 , the second solenoid valve  24 , and the outdoor side control unit  62 . The outdoor side control unit  62  controls the opening and closing of the first solenoid valve  22  and the second solenoid valve  24 . Consequently, the refrigerant that flows through the main refrigerant circuit  30  can be pooled in the refrigerant adjustment vessel  21 . In addition, the outdoor side control unit  62  performs the overfill determination by pooling the refrigerant, with which the main refrigerant circuit  30  is filled, in the refrigerant adjustment vessel  21 . The overfill determination determines whether the main refrigerant circuit  30  is overfilled with the refrigerant by determining whether the refrigerant in the first outdoor side liquid refrigerant piping  15   b  is in the vapor-liquid two-phase state or the liquid phase state. If the main refrigerant circuit  30  is filled with the appropriate amount of the refrigerant, then the refrigerant with which the main refrigerant circuit  30  is filled pools in the refrigerant adjustment vessel  21 , and consequently the refrigerant in the main refrigerant circuit  30  transitions to the insufficient state. Consequently, if the refrigerant flowing through the first outdoor side liquid refrigerant piping  15   b  is in the vapor-liquid two-phase state, then it is determined that the main refrigerant circuit  30  is filled with the appropriate amount of the refrigerant. In addition, if the refrigerant flowing through the first outdoor side liquid refrigerant piping  15   b  is in the liquid phase state, then it is determined that the main refrigerant circuit  30  is overfilled with the refrigerant, namely, that the amount of the refrigerant exceeds the appropriate amount. 
     Thereby, it is determined that the main refrigerant circuit  30  is overfilled with the refrigerant. 
     (2) 
     In the abovementioned embodiment, the diameters of the liquid refrigerant inlet pipe  27  and the overflow pipe  28  are equal to one another and are smaller than the diameters of the pipings that constitute the main refrigerant circuit  30 . Consequently, compared with the case wherein, for example, solenoid valves are provided to the main refrigerant circuit  30 , smaller solenoid valves can be used for the first solenoid valve  22  and the second solenoid valve  24  provided to the liquid refrigerant inlet pipe  27  and the overflow pipe  28 , respectively. 
     Thereby, in this air conditioner  100 , the first solenoid valve  22  and the second solenoid valve  24  cost less than when the solenoid valves are provided to the main refrigerant circuit  30 . 
     (3) 
     In the abovementioned embodiment, the outdoor side control unit  62  makes an overflow determination. The overflow determination determines whether the liquid refrigerant is flowing out of the refrigerant adjustment vessel  21  to the suction side of the compressor  5 . Accordingly, the prescribed amount of the refrigerant with which the main refrigerant circuit  30  is filled can be reliably pooled in the refrigerant adjustment vessel  21 . In addition, the overfill determination, which is made by the outdoor side control unit  62 , determines whether the prescribed amount of the refrigerant with which the main refrigerant circuit  30  is filled is pooled in the refrigerant adjustment vessel  21 . 
     Consequently, the certainty of the overfill determination is improved compared with the case wherein the overfill determination is performed without performing the overflow determination. 
     (4) 
     In the abovementioned embodiment, if a surplus of refrigerant is detected in the main refrigerant circuit  30  during the cooling operation or the heating operation, then the outdoor side control unit  62  sets the first solenoid valve  22  to the open state. Consequently, the refrigerant is guided from the main refrigerant circuit  30  to the refrigerant adjustment unit  20 . In addition, if an insufficient amount of the refrigerant is detected in the main refrigerant circuit  30  during the cooling operation or the heating operation, then the outdoor side control unit  62  sets the third solenoid valve  25  to the open state. Consequently, the refrigerant is guided from the refrigerant adjustment unit  20  to the main refrigerant circuit  30 . 
     Thereby, the amount of the refrigerant flowing through the main refrigerant circuit  30  is regulated in accordance with the excess or insufficiency of the refrigerant flowing therethrough. 
     MODIFIED EXAMPLES 
     In the abovementioned embodiment, the refrigerant overfill determination is made by detecting the temperature of the refrigerant on the upstream side of the outdoor expansion valve  8  and the temperature of the refrigerant on the downstream side of the outdoor expansion valve  8 , and then calculating the difference therebetween. The above notwithstanding, this overfill determination may also be made based on the degree of supercooling on the liquid side of the outdoor heat exchanger  3 . Furthermore, the degree of supercooling on the liquid side of the outdoor heat exchanger  3  is calculated by subtracting the temperature of the refrigerant detected by the expansion valve inlet side temperature sensor  33  from the temperature of the refrigerant detected by the outdoor heat exchanger temperature sensor  32 . In addition, like the abovementioned embodiment, the overfill determination based on the degree of supercooling is made after it is determined that the liquid refrigerant is overflowing from the refrigerant adjustment vessel  21  to the second outdoor side gas refrigerant piping  16   c . Accordingly, if the main refrigerant circuit  30  is filled with the appropriate amount of the refrigerant, then this determination is likewise performed in the state wherein the main refrigerant circuit  30  is filled with an insufficient amount of the refrigerant. 
     If the main refrigerant circuit  30  is filled with the appropriate amount of the refrigerant, then the refrigerant on the liquid side of the outdoor heat exchanger  3  functioning as a condenser has a prescribed degree of supercooling (for example, 3 degree). In addition, if the main refrigerant circuit  30  is filled with an amount of refrigerant that is less than the appropriate amount, then the degree of supercooling becomes less than the prescribed degree of supercooling. If the main refrigerant circuit  30  is filled with the appropriate amount of the refrigerant as discussed above, then this determination is made in the state wherein the main refrigerant circuit  30  is filled with an insufficient amount of the refrigerant. Accordingly, if the calculated degree of supercooling is less than the prescribed degree of supercooling, then it is determined that the main refrigerant circuit  30  is not overfilled with the refrigerant. In addition, if the calculated degree of supercooling is greater than or equal to the prescribed degree of supercooling, then it is determined that the main refrigerant circuit  30  is overfilled with the refrigerant. 
     Thereby, the overfill determination can be made in the main refrigerant circuit  30 . 
     In addition, determining the amount of refrigerant with which the main refrigerant circuit  30  is filled based on the degree of supercooling eliminates the need for the expansion valve outlet side temperature sensor  34  and makes it possible to reduce cost. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, in an air conditioner that comprises a heat source unit, utilization units, and a refrigerant connection piping that connects the heat source unit and the utilization units, it is possible to determine whether the refrigerant circuit is filled with the appropriate amount of refrigerant.