JP2009243842A - Operation method of multiple-type air conditioner and outdoor unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method of a multi-type air conditioner and an outdoor unit for securely performing oil return with indoor comfortability impaired as less as possible. <P>SOLUTION: Openings of expansion valves 20A, 20B of two outdoor heat exchangers 8A, 8B are made to be different from each other. For example, the expansion valve 20A of one outdoor heat exchanger 8A is set to close, and the expansion valve 20B of the other outdoor heat exchanger 8B is set to open. Differential pressure between the high-pressure side and the low-pressure side of refrigerant is increased thereby. Necessary time for returning the refrigerant and lubrication oil to a compressor 5 gets shorter, which means, oil-returning operation time is shortened. As a result, the comfortability is improved by shortening the time during which the air conditioner does not exert heating capacity because of being incapable of performing heating operation and does not provide the indoor comfortability which is its original function. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multi-type air conditioner and a method for operating an outdoor unit.

  As an air conditioner for buildings, there is a multi-type air conditioner in which multiple indoor units are connected to one outdoor unit by gas pipes and liquid pipes, and each indoor unit can perform cooling and heating operations independently. is there.

In the air conditioner, the lubricating oil of the compressor provided in the outdoor unit is discharged from the compressor and stays in the refrigerant gas pipe and the heat exchanger of the indoor unit. For this reason, oil return control is performed to return the accumulated lubricating oil into the compressor.
However, multi-type air conditioners for buildings tend to be complicated because the length of the pipe between the outdoor unit and the indoor unit is long and there are many branches. As a result, oil may accumulate in the piping and the indoor heat exchanger, and the oil may not return to the compressor as expected.

  Particularly during heating, the refrigerant gas pipe has a high pressure, so the flow rate is slow and the lubricating oil tends to stay. Therefore, during heating, oil return control is performed by defrost operation. The defrost operation is an operation of a cooling cycle, and is usually an operation method for melting frost attached to the outdoor heat exchanger during heating operation. By reducing the pressure of the refrigerant gas pipe in this defrost cycle, the gas flow rate is increased and the lubricating oil is less likely to stay.

As oil return control by defrost operation, for example, when replacing an outdoor unit or an indoor unit, there is a method of flowing a liquid refrigerant through a pipe through which the gas refrigerant flows in order to reliably recover the lubricating oil in the pipe through which the gas refrigerant flows. It has been proposed (see, for example, Patent Document 1).
JP 2004-293883 A

However, the method of returning oil by defrost operation has a problem that heating operation cannot be performed while defrost operation is being performed, so that the heating capability cannot be exhibited, and the indoor comfort that is the original function cannot be provided. .
In addition, when oil is returned by defrosting, there is a problem that the refrigerant pressure increases when the heat exchanger of the outdoor unit is not frosted. In the defrost operation, the outdoor fan is not normally operated in order to melt frost, but if the frost does not adhere to the outdoor heat exchanger, the refrigerant does not condense and the refrigerant pressure rises. Therefore, as a workaround, when the refrigerant pressure rises, the outdoor fan is operated to suppress the pressure rise.

  The present invention has been made in view of such circumstances, and provides a multi-type air conditioner and an outdoor unit operating method capable of reliably returning oil without impairing indoor comfort as much as possible. The purpose is to do.

In order to solve the above problems, the multi-type air conditioner of the present invention employs the following means.
That is, the present invention is a multi-type air conditioner including an outdoor unit and a plurality of indoor units, and the outdoor unit includes a compressor, a four-way switching valve, an outdoor heat exchanger, and their An outdoor refrigerant pipe that connects the two, a refrigerant gas pipe that extends from the four-way switching valve to the indoor side, and a refrigerant liquid pipe that extends from the outdoor heat exchanger to the indoor side. When implemented in a cycle, the outdoor heat exchanger switches the four-way switching valve to guide the gas refrigerant discharged from the compressor to the outdoor heat exchanger, and passes from the refrigerant liquid pipe to the indoor unit through the refrigerant gas pipe. When the lubricating oil staying in the pipe and the indoor heat exchanger is returned to the compressor, fan rotational speed control means for controlling the rotational speed of the fan blown to the outdoor heat exchanger is provided. Features.

  When so-called oil return operation is performed in which the lubricating oil staying in the refrigerant gas pipe and the indoor heat exchanger is returned to the compressor, the refrigerant is circulated in the opposite direction to that during heating. At this time, since the outdoor fan is stopped because the control is constructed using the defrost operation, the refrigerant pressure on the high-pressure side is likely to rise when the outdoor heat exchanger is not frosted. If the refrigerant pressure on the high-pressure side rises and the differential pressure with the low-pressure side increases, the oil returns quickly and the oil return operation can be performed quickly. At this time, the refrigerant pressure on the high-pressure side can be adjusted by controlling the rotation speed of the fan that blows air to the outdoor heat exchanger by the fan rotation speed control means.

  Therefore, in the multi-type air conditioner of the present invention, the fan rotation speed control means has a predetermined threshold value for the refrigerant pressure on the high pressure side when the lubricating oil is returned from the refrigerant gas pipe and the heat exchanger of the indoor unit to the compressor. The fan speed is controlled so as to be as follows.

  Thereby, it can suppress that a refrigerant | coolant pressure rises excessively. At this time, if the refrigerant pressure is excessively reduced, the oil return operation takes time. Therefore, it is preferable to control the rotation speed of the fan by the fan rotation speed control means so that the refrigerant pressure is within a predetermined range.

  The multi-type air conditioner of the present invention includes an outdoor unit and a plurality of indoor units, and the outdoor unit connects a compressor, a four-way switching valve, and a plurality of outdoor heat exchangers. An outdoor refrigerant pipe, a refrigerant gas pipe extending from the four-way switching valve to the indoor side, and a refrigerant liquid pipe extending from the outdoor heat exchanger to the indoor side. When an expansion valve for adjusting the refrigerant flow rate is provided and the oil return control for heating is performed in a defrost cycle, the four-way switching valve is switched to guide the gas refrigerant discharged from the compressor to the outdoor heat exchanger, and the refrigerant liquid pipe By passing the refrigerant gas pipe through the indoor unit and returning the lubricating oil staying in the pipe and the indoor heat exchanger to the compressor, at least one expansion valve of the plurality of outdoor heat exchangers is closed. Therefore, the cooling of the entire outdoor heat exchanger It can be characterized by reducing the amount of condensation.

When a plurality of outdoor heat exchangers are provided, when the lubricating oil of the compressor contained in the refrigerant conveyed through the refrigerant gas pipe is returned from the refrigerant gas pipe to the compressor, at least one expansion valve of the plurality of outdoor heat exchangers When the refrigerant is condensed and the condensed amount of refrigerant in the whole of the plurality of outdoor heat exchangers is reduced, the refrigerant pressure on the high pressure side increases, the differential pressure from the low pressure side increases, and the oil return operation can be performed quickly.
Moreover, it is also possible to suppress the refrigerant pressure from rising excessively by adjusting the opening of the expansion valve. Furthermore, since the oil return operation takes time if the refrigerant pressure decreases excessively, it is preferable to adjust and control the opening of the expansion valve so that the refrigerant pressure is within a predetermined range.

  The present invention also includes a compressor, a four-way switching valve, an outdoor heat exchanger, an outdoor refrigerant pipe connecting them, a refrigerant gas pipe extending from the four-way switching valve to the indoor side, and an outdoor heat exchange. A refrigerant liquid pipe extending from the chamber to the indoor side, and when the oil return control for heating is performed in a defrost cycle, the gas discharged from the compressor by switching the four-way switching valve The refrigerant is led to the outdoor heat exchanger, and when the lubricating oil staying in the pipe and the indoor heat exchanger is returned to the compressor by passing through the refrigerant gas pipe and the indoor unit through the refrigerant gas pipe, the refrigerant The number of revolutions of the fan that blows air to the outdoor heat exchanger is controlled so that the refrigerant pressure in the gas pipe is equal to or lower than a predetermined threshold value.

  The present invention also includes a compressor, a four-way switching valve, a plurality of outdoor heat exchangers, an outdoor refrigerant pipe connecting them, a refrigerant gas pipe extending from the four-way switching valve to the indoor side, an outdoor When operating the oil return control of the heating in the defrost cycle with the refrigerant liquid pipe extended from the heat exchanger to the indoor side, the four-way switching valve is switched to discharge from the compressor When the lubricating oil staying in the pipe and the indoor heat exchanger is returned to the compressor by introducing the gas refrigerant to the outdoor heat exchanger, passing through the indoor unit through the refrigerant liquid pipe and the refrigerant gas pipe The amount of refrigerant condensed in the plurality of outdoor heat exchangers as a whole is reduced by blocking the flow of the refrigerant to at least one of the plurality of outdoor heat exchangers.

Thereby, the refrigerant | coolant pressure of the said refrigerant | coolant of a high voltage | pressure side can be raised by reducing the amount of refrigerant | coolants condensed, and efficiency improvement of an oil return operation | movement can be aimed at.

According to the present invention, if the refrigerant pressure on the high pressure side increases and the differential pressure with the low pressure side increases, the oil return operation can be performed quickly. As a result, the heating operation cannot be performed because the heating operation cannot be performed, and the time during which the indoor comfort that is the original function cannot be provided can be shortened and the comfort can be improved.
At this time, it is possible to suppress the refrigerant pressure from rising excessively by controlling the fan rotation speed of the outdoor heat exchanger. Further, since the oil return operation takes time if the refrigerant pressure is excessively reduced, the fan rotation speed control means can also control the fan rotation speed so that the refrigerant pressure is within a predetermined range.

Further, according to the present invention, by closing at least one of the expansion valves of the plurality of outdoor heat exchangers, the amount of condensation in the outdoor heat exchanger can be reduced, and the high pressure side of the refrigerant pressure can be increased. The pressure difference with the low pressure side becomes large, and the oil return operation can be performed quickly. As a result, the heating operation cannot be performed because the heating operation cannot be performed, and the time during which the indoor comfort that is the original function cannot be provided can be shortened and the comfort can be improved.

[First embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a refrigerant circuit diagram of a multi-type heat pump air conditioner 1 according to the present embodiment.
The multi-type heat pump air conditioner 1 has a configuration in which a plurality of indoor units (not shown) are connected in parallel to a single outdoor unit (outdoor unit) 2. In the present embodiment, the number of indoor units connected is not particularly limited, and at least two indoor units are connected.

  The outdoor unit 2 includes a compressor 5, a discharge pipe 4 </ b> A connected to the compressor 5, a four-way switching valve 7 connected to the first port 7 </ b> A, and a refrigerant pipe 4 </ b> B to the second port 7 </ b> B of the four-way switching valve 7. Two outdoor heat exchangers 8A and 8B connected through the refrigerant, a refrigerant liquid pipe 4C extending from the outdoor heat exchangers 8A and 8B to the indoor unit (not shown) side, and a third of the four-way switching valve 7 The refrigerant gas pipe 4D extended from the port 7C to the indoor unit (not shown) side and the fourth port 7D of the four-way switching valve 7 are connected via the suction pipe 4E, and the suction pipe 4F is connected to the compressor 5. And an accumulator 10 connected to each other via the discharge pipes 4A to 4F as described above to constitute a circuit of the outdoor refrigerant pipe.

The outdoor heat exchangers 8A and 8B are provided with expansion valves 20A and 20B, respectively.
The refrigerant liquid pipe 4C is provided with a receiver 12 for storing liquid refrigerant and a double pipe heat exchanger 13 for providing supercooling during cooling.

  Next, the effect | action of the multi-type heat pump type air conditioner 1 concerning this embodiment is demonstrated. Note that the operation and operation of the multi-type heat pump air conditioner 1 described below is performed by a control unit (not shown) in accordance with the selection of an operation mode such as cooling operation or heating operation by the user. It is automatically performed by controlling each part of the machine 1.

  First, the cooling operation will be described. During cooling, the four-way switching valve 7 is switched to a state in which the first port 7A and the second port 7B, and the third port 7C and the fourth port 7D communicate with each other. Thereby, the high-temperature and high-pressure refrigerant gas compressed by the compressor 5 flows into the outdoor heat exchangers 8A and 8B through the discharge pipe 4A, the four-way switching valve 7, and the refrigerant pipe 4B. This refrigerant exchanges heat with the outside air in the outdoor heat exchangers 8A and 8B, dissipates heat to the outside air, and is condensed and liquefied. The liquefied refrigerant flows in one direction in the refrigerant liquid pipe 4 </ b> C and flows into the receiver 12.

The refrigerant flowing out from the receiver 12 is cooled while passing through the double-pipe heat exchanger 13, and is further subcooled.
The refrigerant evaporated in the inner pipe 13A of the double pipe heat exchanger 13 is sent into the accumulator 10 through the pipe 16 from the outlet.

On the other hand, the refrigerant that has been supercooled in the double pipe heat exchanger 13 flows to the indoor unit (not shown) through the refrigerant liquid pipe 4C. The refrigerant that has flowed into the indoor unit (not shown) flows into the indoor heat exchanger (not shown) of the indoor unit and is heat-exchanged with the indoor air circulated to the indoor heat exchanger to cool the indoor air. This is subject to cooling.
The refrigerant evaporated by cooling the indoor air in the indoor heat exchanger (not shown) returns to the outdoor unit 2 again through the refrigerant gas pipe 4D, and the four-way switching valve 7, the suction pipe 4E, the accumulator 10, and the suction pipe. It is sucked into the compressor 5 through 4F. The cooling operation is performed by repeating this refrigerant circulation cycle.

  Subsequently, the heating operation will be described. During heating, the four-way switching valve 7 is switched to a state in which the first port 7A and the third port 7C, and the second port 7B and the fourth port 7D communicate with each other. Thereby, the high-temperature and high-pressure refrigerant gas compressed by the compressor 5 flows into each indoor unit (not shown) through the discharge pipe 4A, the four-way switching valve 7, and the refrigerant gas pipe 4D. The refrigerant flowing into the indoor unit (not shown) is heat-exchanged with indoor air circulated by a fan (not shown) in an indoor heat exchanger (not shown) to heat the indoor air. This room air is used for heating.

The refrigerant condensed and liquefied by radiating heat to the indoor air with an indoor heat exchanger (not shown) returns to the outdoor unit 2 again through the refrigerant liquid pipe 4C. The refrigerant that has returned to the outdoor unit 2 flows in one direction in the refrigerant liquid pipe 4 </ b> C and flows into the receiver 12.
The refrigerant that flows out of the receiver 12 flows into the outdoor heat exchangers 8A and 8B, absorbs heat from the outside air, and is evaporated. Thereafter, the refrigerant is sucked into the compressor 5 through the refrigerant pipe 4B, the four-way switching valve 7, the suction pipe 4E, the accumulator 10, and the suction pipe 4F. The heating operation is performed by repeating this refrigerant circulation cycle.

In the outdoor unit 2 as described above, in the oil return operation during the heating operation, after flowing out from the compressor 5, the lubricating oil staying in the refrigerant gas pipe 4 </ b> D or the indoor heat exchanger is returned to the compressor 5. This is done by defrost operation. In this case, in order to prevent cold air from being generated by a control unit (not shown), first, a fan (not shown) of the indoor unit is stopped. Thereby, indoor air-conditioning at the time of oil return operation is stopped. The four-way switching valve 7 is switched to a state in which the first port 7A and the second port 7B, and the third port 7C and the fourth port 7D are communicated with each other. As a result, the high-temperature and high-pressure gas refrigerant compressed by the compressor 5 is guided to the outdoor heat exchangers 8A and 8B, and is passed through the refrigerant gas pipe 4D from the refrigerant liquid pipe 4C and through the refrigerant gas pipe 4D. Led to.
The refrigerant and lubricating oil that have flowed into the outdoor unit 2 flow through the four-way switching valve 7, flow into the suction pipe 4 </ b> E, and are returned to the compressor 5 through the accumulator 10. As a result, the lubricating oil retained in the refrigerant gas pipe 4D and the indoor heat exchanger can be returned to the compressor 5.

When the oil return operation is performed, the outdoor heat exchangers 8A and 8B are often not frosted. In such a case, the refrigerant pressure tends to increase on the high pressure side (the discharge side of the compressor 5). As a result, the differential pressure between the high pressure side and the low pressure side (the suction side of the compressor 5) increases, so the time required for the refrigerant and lubricating oil to return to the compressor 5 is shortened, that is, the oil return operation time is shortened. It becomes possible to do.
If the refrigerant pressure on the high pressure side is increased, the efficiency of the oil return operation can be increased. However, if the refrigerant pressure is excessively increased, a sensor or the like that monitors the refrigerant pressure detects that the refrigerant pressure is abnormal. Sometimes. When the refrigerant pressure becomes abnormal, the oil return operation itself stops.
Therefore, in the present embodiment, when the oil return operation is performed, the fans 30A and 30B provided in the outdoor heat exchangers 8A and 8B are detected so that the refrigerant pressure is not excessively increased while detecting the refrigerant pressure at 4A. Is controlled by a control unit (fan speed control means) (not shown). If the outdoor heat exchangers 8A and 8B are cooled by the rotation of the fans 30A and 30B, it is possible to suppress an excessive increase in pressure.

For example, as shown in FIG. 2, after the oil return operation is started (t1 in the figure), when the refrigerant pressure reaches a predetermined threshold value S1 (t2 in the figure), the fans 30A of the outdoor heat exchangers 8A and 8B, 30B is rotated to prevent the refrigerant pressure from rising.
On the other hand, in order to shorten the oil return operation, it is preferable to increase the refrigerant pressure on the high pressure side as much as possible as described above. Therefore, if the monitored refrigerant pressure reaches a predetermined threshold value S1 so that the refrigerant pressure falls within a predetermined range with the threshold value S1 as the upper limit, the rotation speed of the fans 30A and 30B is increased, It is also preferable to reduce the rotational speed of the fans 30A and 30B if it deviates downward from the lower limit of this range.
Thereby, it is possible to perform the oil return operation while maintaining high efficiency while preventing the refrigerant pressure from rising excessively.

As described above, according to the multi-type heat pump air conditioner 1 according to the present embodiment, the following operational effects can be obtained.
Thereby, the refrigerant differential pressure on the high-pressure side and the low-pressure side is increased, and the time required for the refrigerant and the lubricating oil to return to the compressor 5 is shortened, that is, the oil return operation time can be shortened. As a result, the heating operation cannot be performed because the heating operation cannot be performed, and the time during which the indoor comfort that is the original function cannot be provided can be shortened and the comfort can be improved. At this time, the fans 30A and 30B provided in the outdoor heat exchangers 8A and 8B are rotated so that the pressure of the liquid refrigerant on the high pressure side is excessively increased by controlling the refrigerant pressure not to be excessively high. The oil return operation time can be shortened while preventing pressure abnormalities and the like.

[Second Embodiment]
Next, a second embodiment according to the present invention will be described.
The configuration shown in the second embodiment below controls the flow rates of the two outdoor heat exchangers 8A and 8B instead of the control using the fans 30A and 30B shown in the first embodiment. Yes, the configuration other than the portions related to it is the same as that shown in the first embodiment. In the following, differences from the first embodiment will be mainly described, and the same reference numerals will be given to common configurations, and description thereof will be omitted.
In the multi-type heat pump type air conditioner 1 shown in FIG. 1, when the oil return operation is performed during the heating operation, the expansion valves 20A and 20B of the two outdoor heat exchangers 8A and 8B are controlled by a control unit (not shown). Make the opening different from each other. For example, the expansion valve 20A of one outdoor heat exchanger 8A is closed and the expansion valve 20B of the other outdoor heat exchanger 8B is opened.

Thereby, according to the multi-type heat pump type air conditioner 1 concerning this embodiment, there exist the following effects.
In the multi-type heat pump air conditioner 1, the apparent capacity of the condenser that condenses the gas refrigerant into the liquid refrigerant is reduced. Then, the refrigerant pressure rises on the high pressure side, and the differential pressure between the refrigerant on the high pressure side and the low pressure side increases. As a result, the time required for the refrigerant and the lubricating oil to return to the compressor 5 is shortened, that is, the oil return operation time can be shortened. As a result, the heating operation cannot be performed because the heating operation cannot be performed, and the time during which the indoor comfort that is the original function cannot be provided can be shortened and the comfort can be improved.

In each embodiment described above, each part of the multi-type heat pump type air conditioner 1 has been described. However, the present invention is not limited to this, and for example, an indoor unit (not shown) or the like adopts any configuration. May be.
In addition, other configurations can be appropriately combined to improve the cooling / heating capacity, increase the efficiency of the oil return operation, and the like.

It is a figure which shows the structure of the outdoor unit of the multi-type heat pump type air conditioner concerning embodiment of this invention. It is a figure which shows the example of fan rotation speed control according to a refrigerant | coolant pressure.

Explanation of symbols

1 Multi-type heat pump air conditioner 2 Outdoor unit (outdoor unit)
4A Discharge piping (outdoor cooling piping)
4B Refrigerant piping (outdoor cooling piping)
4C Refrigerant liquid pipe (outdoor cooling piping)
4D refrigerant gas pipe (outdoor cooling pipe)
4E Suction piping (outdoor cooling piping)
4F Suction piping (outdoor cooling piping)
5 Compressor 7 Four-way switching valve 8A, 8B Outdoor heat exchanger 10 Accumulator 12 Receiver 13 Double pipe heat exchanger 20A, 20B Expansion valve 30A, 30B Fan

Claims (6)

A multi-type air conditioner comprising an outdoor unit and a plurality of indoor units,
The outdoor unit is
A compressor, a four-way switching valve, an outdoor heat exchanger, an outdoor refrigerant pipe connecting them, a refrigerant gas pipe extending from the four-way switching valve to the indoor side, and an indoor side from the outdoor heat exchanger A refrigerant liquid pipe extended to
When the oil return control of heating is performed in a defrost cycle, the refrigerant gas discharged from the compressor by switching the four-way switching valve is guided to the outdoor heat exchanger, and the refrigerant gas passes through the indoor unit from the refrigerant liquid pipe. Fan rotation speed control means is provided for controlling the rotation speed of the fan that blows air to the outdoor heat exchanger when the lubricating oil staying in the pipe and the indoor heat exchanger is returned to the compressor through the pipe. A multi-type air conditioner characterized by   The fan rotational speed control means controls the rotational speed of the fan so that the refrigerant pressure is equal to or lower than a predetermined threshold when returning the lubricating oil from the refrigerant pipe and the indoor heat exchanger to the compressor. The multi-type air conditioner according to claim 1. A multi-type air conditioner comprising an outdoor unit and a plurality of indoor units,
The outdoor unit is
A compressor, a four-way switching valve, a plurality of outdoor heat exchangers, an outdoor refrigerant pipe connecting them, a refrigerant gas pipe extending indoors from the four-way switching valve, and the outdoor heat exchanger A refrigerant liquid pipe extended to the indoor side,
When the oil return control for heating is performed in a defrost cycle, the plurality of outdoor heat exchangers each include an expansion valve that adjusts the refrigerant flow rate in each, and the gas refrigerant discharged from the compressor is switched by switching the four-way switching valve. When the lubricating oil staying in the pipe and the indoor heat exchanger is returned to the compressor by guiding to the outdoor heat exchanger and passing through the refrigerant gas pipe from the refrigerant liquid pipe through the indoor unit, a plurality of By closing at least one expansion valve of the outdoor heat exchanger, the multi-type air conditioner reduces the amount of refrigerant condensed in the plurality of outdoor heat exchangers as a whole. A compressor, a four-way switching valve, an outdoor heat exchanger, an outdoor refrigerant pipe connecting them, a refrigerant gas pipe extending from the four-way switching valve to the indoor side, and an indoor side from the outdoor heat exchanger An operation method of an outdoor unit comprising a refrigerant liquid pipe extended to
When the oil return control of heating is performed in a defrost cycle, the refrigerant gas discharged from the compressor by switching the four-way switching valve is guided to the outdoor heat exchanger, and the refrigerant gas passes through the indoor unit from the refrigerant liquid pipe. When the lubricating oil staying in the pipe and the indoor heat exchanger is returned to the compressor through the pipe, air is blown to the outdoor heat exchanger so that the refrigerant pressure on the high-pressure side is equal to or lower than a predetermined threshold. A method for operating an outdoor unit, characterized in that the number of rotations of a fan is controlled. A compressor, a four-way switching valve, a plurality of outdoor heat exchangers, an outdoor refrigerant pipe connecting them, a refrigerant gas pipe extending indoors from the four-way switching valve, and the outdoor heat exchanger An operation method of an outdoor unit including a refrigerant liquid pipe extended to an indoor side,
When the oil return control of heating is performed in a defrost cycle, the refrigerant gas discharged from the compressor by switching the four-way switching valve is guided to the outdoor heat exchanger, and the refrigerant gas passes through the indoor unit from the refrigerant liquid pipe. By passing through the pipe, when returning the lubricating oil staying in the pipe and the indoor heat exchanger to the compressor, by blocking the flow of the refrigerant to at least one of the plurality of outdoor heat exchangers, A method for operating an outdoor unit, characterized in that the amount of refrigerant condensed in the whole of the plurality of outdoor heat exchangers is reduced. The method for operating the outdoor unit according to claim 5, wherein the refrigerant pressure of the refrigerant on the high-pressure side is increased by reducing the amount of condensation of the refrigerant.

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