JP7067864B2 - Air conditioner - Google Patents

Description

The present invention relates to a technique for controlling a refrigerating cycle of an air conditioner.

In an air conditioner, it is desirable to fill a predetermined amount of refrigerant according to the length of the pipe to be constructed, but in order to shorten the work time during construction, a tank for storing excess refrigerant is provided and the predetermined pipe length is provided. The amount of refrigerant corresponding to the above may be sealed before shipping.
If the construction pipe length is short, the air conditioner will hold more refrigerant than necessary, and there is a concern that the discharge pressure will rise and the liquid will return to the compressor. The amount of refrigerant is adjusted.

In recent years, the length of construction pipes has tended to increase, and it is necessary to increase the size of the tank for storing excess refrigerant. The larger the volume of this tank, the more excess refrigerant can be stored, but the larger the volume of the tank, the higher the cost, which leads to an increase in the cost of the air conditioner. Therefore, an inexpensive tank is used as the minimum required volume of the tank, and the refrigerating cycle of the air conditioner is controlled to suppress the occurrence of abnormalities caused by the excess of refrigerant.
For example, in Patent Document 1, when it is determined that the connecting pipe is a short pipe, the rotation speed of the compressor is reduced by using the discharge pressure value and the discharge pressure rise time, and the discharge pressure rises due to the excess refrigerant. Is disclosed to suppress.

Japanese Unexamined Patent Publication No. 2016-17729

According to the above-mentioned prior art, when the discharge pressure rises, the compressor rotation speed is lowered to suppress the rise in the discharge pressure. However, when the rotation speed of the compressor drops sharply, the excess refrigerant accumulated in the condenser flows into the evaporator, and finally the two-phase refrigerant (gas / liquid mixed refrigerant) may flow into the suction side of the compressor. be. As a result, the compressor may be liquid-compressed, leading to a compressor failure. In addition, there is a risk that the compressor protection device will operate due to a significant increase in discharge pressure, causing an emergency stop.

An object of the present invention is to provide an air conditioner capable of suppressing an increase in discharge pressure due to an excess of refrigerant and suppressing liquid return of the refrigerant to a compressor.

In order to solve the above problems, the air conditioner of the present invention includes a control unit that controls the refrigeration cycle of the air conditioner, and the control unit determines whether or not the discharge pressure of the compressor is equal to or higher than a predetermined pressure control value. When the discharge pressure is equal to or higher than the predetermined pressure control value, the rotation speed of the compressor is reduced to reduce the amount of refrigerant flowing into the heat exchanger serving as the condenser, and the outdoor expansion valve. When the valve opening degree of the compressor is increased, the refrigerant accumulated in the heat exchanger serving as the condenser is discharged from the heat exchanger, and the discharge superheat degree or suction superheat degree of the compressor refrigerant is equal to or less than a predetermined value, the above- mentioned The valve opening of the enlarged outdoor expansion valve was reduced.
Other means for solving the problem will be described in the form for carrying out the invention.

According to the present invention, it is possible to provide an air conditioner capable of suppressing an increase in discharge pressure without sucking liquid refrigerant even when excess refrigerant is generated.

It is a block diagram of the air conditioner of an embodiment. It is a control flow chart by the discharge superheat degree. It is a figure which shows the outline of the time change of the discharge pressure by the control flow of FIG. It is a figure which shows the outline of the time change of the discharge superheat degree by the control flow of FIG. It is a control flow diagram by a suction superheat degree. It is a figure which shows the outline of the time change of the discharge pressure by the control flow of FIG. It is a figure which shows the outline of the time change of the inhalation superheat degree by the control flow of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an air conditioner 100 that performs air conditioning by a refrigerating cycle operation of cooling / heating according to an embodiment.
In FIG. 1, the direction in which the refrigerant flows during the heating operation is shown by a solid line, and the direction in which the refrigerant flows during the cooling operation is shown by a broken line.

The air conditioner 100 includes an outdoor unit Ho and an indoor unit Hi connected by a gas connection pipe 40 and a liquid connection pipe 41.
A gas-side blocking valve V1 is provided on the outdoor unit Ho side of the gas connection pipe 40, and a liquid-side blocking valve V2 is provided on the outdoor unit Ho side of the liquid connection pipe 41. The gas-side blocking valve V1 and the liquid-side blocking valve V2 are opened after the installation work of the air conditioner 100, so that the refrigerant sealed in the outdoor unit Ho at the time of shipment is combined with the indoor unit Hi and the gas connection pipe 40. It is filled with the liquid connection pipe 41.

The refrigerating circuit of the air conditioner 100 of the embodiment includes a compressor 10, a four-way valve 11, an indoor heat exchanger 12, an outdoor expansion valve 13, an outdoor heat exchanger 14, and an accumulator that separates gas and liquid from the refrigerant. It is composed of 15 and a tank 16 for storing excess refrigerant generated during operation.
More specifically, the accumulator 15 is provided on the suction side of the compressor 10 so that the compressor 10 sucks the liquid refrigerant and separates the gas and liquid so as not to cause the compressor failure, and the condensed liquid is installed. It is also a refrigerant amount adjuster that stores the refrigerant and adjusts it to an appropriate amount of refrigerant.
Therefore, a refrigeration circuit without a tank 16 for storing the refrigerant may be used.

The compressor 10 is a device that compresses a gas refrigerant. The type of the compressor 10 is not particularly limited, and a scroll type, rotary type, screw type or the like compressor can be used.
The four-way valve 11 is a valve that switches the flow direction of the refrigerant between the cooling operation and the heating operation.

Next, the refrigeration cycle during the cooling operation will be described.
During the cooling operation, the refrigerant is compressed by the compressor 10, and the compressed gas refrigerant flows into Go on the gas side of the outdoor heat exchanger 14. The compressed gas refrigerant is heat-exchanged between the outside air and the refrigerant by the outdoor fan Fo in the outdoor heat exchanger 14, condenses and becomes a liquid refrigerant, which flows out from Lo on the liquid side of the outdoor heat exchanger 14 and is indoors. It flows into Li on the liquid side of the heat exchanger 12.
In the indoor heat exchanger 12, heat is exchanged between the indoor air (air in the air-conditioned space) and the refrigerant by the indoor fan Fi, and the liquid refrigerant evaporates to become a gas refrigerant, which is on the gas side of the indoor heat exchanger 12. It is discharged from Gi and sucked into the suction side of the compressor 10.

Next, the refrigeration cycle during the heating operation will be described.
During the heating operation, the four-way valve 11 is switched in the direction opposite to that during the cooling operation (solid line), and the gas refrigerant compressed by the compressor 10 flows into Gi on the gas side of the indoor heat exchanger 12. The compressed gas refrigerant exchanges heat between the indoor air (air in the air-conditioned space) and the refrigerant by the indoor fan Fi, condenses and becomes a liquid refrigerant, and flows out from Li on the liquid side of the indoor heat exchanger 12. Then, it flows into Lo on the liquid side of the outdoor heat exchanger 14.
In the outdoor heat exchanger 14, heat is exchanged between the outside air and the refrigerant by the outdoor fan Fo, and the liquid refrigerant evaporates to become a gas refrigerant, which is discharged from Go on the gas side of the outdoor heat exchanger 14 and is discharged from the Go of the compressor 10. It is inhaled to the inhalation side.

By switching the four-way valve 11 in this way, the discharge side of the compressor 10 is connected to the outdoor heat exchanger 14 and the suction side is connected to the indoor heat exchanger 12 during the cooling operation. During the heating operation, conversely, the discharge side of the compressor 10 is connected to the indoor heat exchanger 12, and the suction side is connected to the outdoor heat exchanger 14.
The outdoor expansion valve 13 is a valve for reducing the pressure of the liquid refrigerant and adjusting the flow rate of the refrigerant flowing through the indoor heat exchanger 12 or the outdoor heat exchanger 14. Regarding the valve opening of the outdoor expansion valve in the following description (including the drawing), "open" means to "increase" the valve opening, and "closed" means to "decrease" the valve opening. It shall be.

The air conditioner 100 of the present embodiment is a detection result of the temperature sensor T or the pressure sensor P, which will be described later, in order to suppress an increase in the discharge pressure without the compressor sucking the liquid refrigerant even when a surplus refrigerant is generated. An outdoor unit control device 30 that controls the rotation speed of the compressor 10 and the valve opening degree of the outdoor expansion valve 13 is provided.
The indoor unit control device 31 controls the indoor fan Fi based on the information received from the outdoor unit control device 30.

Specifically, the control unit 30a of the outdoor unit control device 30 has a pressure control value of the refrigerant on the discharge side of the compressor 10 stored in the storage unit 30b, a target value of the degree of superheat of the refrigerant, and a temperature sensor T (suction temperature). Based on the detection result of the sensor T20 or the discharge temperature sensor T22) or the pressure sensor P (suction pressure sensor P21 or the discharge pressure sensor P23), the rotation speed of the compressor 10 and the valve opening degree of the outdoor expansion valve 13 are controlled.
The degree of superheat of the refrigerant is a numerical value indicating the temperature difference between the saturation temperature corresponding to the pressure of the refrigerant and the refrigerant. Hereinafter, the degree of refrigerant superheat on the suction side of the compressor 10 is referred to as “suction superheat”, and the degree of refrigerant superheat on the discharge side of the compressor 10 is referred to as “discharge superheat”.

As the temperature sensor or pressure sensor referred to by the control unit 30a, the following sensors are appropriately selected.
The suction temperature sensor T20 is a sensor that detects the temperature (suction temperature) of the refrigerant sucked into the compressor 10, and is installed near the suction port of the compressor 10.
The suction pressure sensor P21 is a sensor that detects the pressure (suction pressure) of the refrigerant sucked into the compressor 10, and is installed near the suction port of the compressor 10.
The discharge temperature sensor T22 is a sensor that detects the temperature (discharge temperature) of the refrigerant discharged from the compressor 10, and is installed near the discharge port of the compressor 10.
The discharge pressure sensor P23 is a sensor that detects the pressure (discharge pressure) of the refrigerant discharged from the compressor 10, and is installed near the discharge port of the compressor 10.

Further, the air conditioner 100 includes an indoor suction temperature sensor (not shown) for detecting the indoor temperature, an indoor blowout temperature sensor (not shown) for detecting the temperature blown out from the indoor unit, and an outdoor temperature for detecting the outdoor temperature. It is also equipped with a sensor (not shown) and an outdoor liquid pipe temperature sensor (not shown) that detects the temperature of the liquid pipe of the outdoor heat exchanger.

The outdoor unit control device 30 may control the compressor 10, the four-way valve 11, the outdoor expansion valve 13, and the outdoor fan Fo based on a signal received from a remote controller (not shown) via the indoor unit Hi.

Next, with reference to FIG. 2, a control flow based on the refrigerant superheat degree of the “discharge superheat degree” of the control unit 30a that controls the rotation speed of the compressor 10 and the valve opening degree of the outdoor expansion valve 13 will be described.
In the air conditioner 100, when the liquid refrigerant is stored in the refrigerant condenser (indoor heat exchanger 12 during heating operation or outdoor heat exchanger 14 during cooling operation), the effective heat exchange area is reduced. The amount of heat exchanged is reduced. To compensate for this, the rotation speed of the compressor 10 increases so that the inflow of the refrigerant increases, so that the discharge pressure of the compressor 10 rises.

In step S21, the control unit 30a of the outdoor unit control device 30 of the embodiment detects the pressure (discharge pressure) of the refrigerant discharged from the compressor 10 by the discharge pressure sensor P23 which is the discharge pressure detecting means, and discharges the pressure (discharge pressure). It is determined whether or not the pressure is P1 or more, which is the pressure control value of the storage unit 30b.
Here, P1 determines whether or not a surplus refrigerant is generated and the surplus refrigerant is stored in the condenser in an expected amount or more when the pipe is constructed in a state shorter than the pipe length assumed by the air conditioner 100 of the embodiment. The discharge pressure value to be applied.

When the discharge pressure is smaller than P1 (No in S21), it is determined that no surplus refrigerant is generated, and the process is terminated.
When the discharge pressure is P1 or more (Yes in S21), the rotation speed of the compressor 10 is controlled to be reduced by a predetermined amount so that the discharge pressure is lowered (S22).
Then, control is performed to open (increase) the valve opening degree of the outdoor expansion valve 13 so that the surplus refrigerant stored in the condenser is discharged from the condenser (S23).

Next, the control unit 30a subtracts the saturation temperature corresponding to the discharge pressure of the refrigerant detected by the discharge pressure sensor P23 from the temperature of the discharge refrigerant of the compressor 10 detected by the discharge temperature sensor T22, and the discharge superheat degree of the refrigerant. Is calculated. Then, it is determined whether or not the calculated discharge superheat degree is equal to or less than the value of the first setting threshold value T1 (S24).

The control unit 30a determines whether or not the refrigerant sucked by the compressor 10 contains an excess liquid refrigerant by the first set threshold value T1. This is because when the compressor 10 sucks in a refrigerant containing a small amount of liquid refrigerant and performs the compression operation, the degree of superheat decreases due to the heat of vaporization of the liquid refrigerant. That is, when the discharge superheat degree is small, it is considered that the refrigerant containing the excess liquid refrigerant has been sucked in. Therefore, by comparing the calculated discharge superheat degree with the first set threshold value T1, the compressor 10 is supplied. The liquid return can be determined.

In step S24, when the discharge superheat degree ≦ T1 (Yes in S24), it is determined that the liquid has returned to the compressor 10, and the process proceeds to step S25.
When the discharge superheat degree> T1 (No in S24), the process returns to step S22, and the discharge pressure is continuously reduced (S22) and the excess refrigerant is discharged (S23).

In step S25, in order to prevent the liquid from returning to the compressor 10, the valve opening degree of the outdoor expansion valve 13 is controlled to be closed (reduced) . As a result, the flow rate of the refrigerant decreases, so that the liquid refrigerant does not flow into the accumulator 15 and the compressor 10, and the liquid return stops.

Next, in step S26. The control unit 30a detects the pressure (discharge pressure) of the refrigerant discharged from the compressor 10 by the discharge pressure sensor P23, and whether or not this discharge pressure is P2 or less, which is the pressure control value of the storage unit 30b. Is determined.
If the discharge pressure is higher than P2 (No in S26), the process returns to step S22, and the decrease in discharge pressure (S22) and the discharge of excess refrigerant (S23) are continued.

If the discharge pressure is P2 or less, which is the pressure control value of the storage unit 30b (Yes in S26), the control flow processing is terminated. Here, P2, which is a pressure control value, is a lower limit value of the pressure range in the compressor 10 during operation.

In the above description, an example of detecting the discharge pressure of the compressor 10 by the discharge pressure sensor P23 has been shown, but the pressure estimated from the condensation temperature of the condenser may be used as the discharge pressure of the compressor 10.
Further, the discharge pressure value may be determined by a pressure shutoff device that operates at the pressure control value P1 or the pressure control value P2.

The outline of the time change of the discharge pressure by the control flow of FIG. 2 is shown in FIG. 3A, and the outline of the time change of the discharge superheat degree is shown in FIG. 3B.
FIG. 3A is a diagram showing a time change of the discharge pressure of the compressor 10 with the horizontal axis as the operating time and the vertical axis as the pressure.

During the heating operation of the air conditioner 100 in which the short pipe is constructed according to the embodiment, when excess refrigerant is generated and the liquid refrigerant that cannot be stored begins to accumulate in the indoor heat exchanger 12, the operation time elapses as shown in FIG. 3A. At the same time, the discharge pressure of the compressor 10 rises.
When the discharge pressure reaches P1, the control unit 30a reduces the rotational speed of the compressor 10 in step S21 of FIG. 2, so that the discharge pressure decreases to a value smaller than P1.

When the discharge pressure drops to P2, the control unit 30a ends the process in step S26 of FIG. 2, so that the rotation speed of the compressor 10 does not decrease and the decrease in the discharge pressure stops.
After that, the compressor 10 is operated with the discharge pressure adjusted to be smaller than P1 and in the range of P2 or more.

FIG. 3B is a diagram showing a time change of the discharge superheat degree of the compressor 10 with the horizontal axis as the operating time and the vertical axis as the superheat degree.
Similar to the description of FIG. 3A, the discharge superheat degree increases in conjunction with the discharge pressure of the compressor 10 with the lapse of the operation time.

As described with reference to FIG. 3A, when the discharge pressure reaches P1, the control unit 30a reduces the rotational speed of the compressor 10 by step S21 of FIG. At this time, since the control unit 30a opens the valve opening degree of the outdoor expansion valve in step S23 of FIG. 2, the refrigerant flow rate increases and discharges as shown in FIG. 3B in synchronization with the pressure drop in FIG. 3A. The degree of overheating decreases.

When the discharge superheat degree drops to T1, the control unit 30a closes the valve opening degree of the outdoor expansion valve in step S25 of FIG. 2, so that the refrigerant flow rate decreases and the discharge superheat degree starts to increase.
After that, the compressor 10 is operated in a state where the discharge superheat degree is higher than T1 and there is no liquid return.

In the above, when the rotation speed of the compressor 10 is reduced and the valve opening of the outdoor expansion valve is opened to reduce the discharge pressure, the degree of overheating of the discharge is detected to detect the liquid return of the compressor. Explained. Next, a method of controlling the rotation speed of the compressor 10 and the valve opening degree of the outdoor expansion valve 13 by the suction superheat degree of the compressor 10 instead of the discharge superheat degree of the compressor 10 is based on the suction superheat degree of FIG. This will be described with reference to the control flow diagram.

The control flow of FIG. 4 differs from the control flow of FIG. 2 only in step S44. Therefore, the description other than step S44 will be omitted here.
In step S44, the control unit 30a subtracts the saturation temperature corresponding to the suction pressure of the refrigerant detected by the suction pressure sensor P21 from the suction temperature of the refrigerant of the compressor 10 detected by the suction temperature sensor T20, and overheats the suction of the refrigerant. Calculate the degree. Then, it is determined whether or not the calculated inhalation superheat degree is equal to or less than the value of the second set threshold value T2.

In the above, the suction superheat degree is calculated from the suction pressure of the refrigerant detected by the suction pressure sensor P21, but the suction superheat degree may be calculated from the pressure estimated from the evaporation temperature on the evaporator side.

The control unit 30a determines whether or not the refrigerant sucked by the compressor 10 contains an excess liquid refrigerant by the second set threshold value T2.
This is because the liquid refrigerant flowing out of the condenser by opening (increasing) the valve opening of the outdoor expansion valve in step S23 may cause excess refrigerant to flow into the evaporator in excess of the amount stored in the tank 16. be. In the evaporator, the excess liquid refrigerant flows in, so that the refrigerant from the evaporator is sucked into the compressor 10 in a state where the degree of superheat is low. Further, the amount of the liquid refrigerant stored in the accumulator 15 is exceeded, and the gas-liquid separation of the refrigerant is not sufficiently performed, so that the liquid refrigerant is mixed in the refrigerant sucked into the compressor 10.
By comparing the calculated suction superheat degree with the second set threshold value T2, it is possible to determine the liquid return to the compressor 10.

In step S44, the control unit 30a determines that the liquid has returned to the compressor 10 when the suction superheat degree ≦ T2 (Yes in S44), and proceeds to step 25.
When the suction superheat degree> T2 (No in S44), the process returns to step S22, and the decrease in discharge pressure (S22) and the discharge of excess refrigerant (S23) are continued.

The outline of the time change of the discharge pressure by the control flow of FIG. 4 is shown in FIG. 5A, and the outline of the time change of the suction superheat degree is shown in FIG. 5B.
FIG. 5A is a diagram showing a time change of the discharge pressure of the compressor 10 with the horizontal axis as the operating time and the vertical axis as the pressure.

During the heating operation of the air conditioner 100 in which the short pipe is constructed according to the embodiment, excess refrigerant is generated, and when the refrigerant that cannot be stored begins to accumulate in the indoor heat exchanger 12, as shown in FIG. 5A, as the operation time elapses. The discharge pressure of the compressor 10 rises.
When the discharge pressure reaches P1, the control unit 30a reduces the rotational speed of the compressor 10 in step S21 of FIG. 4, so that the discharge pressure decreases to a value smaller than P1.

When the discharge pressure drops to P2, the control unit 30a ends the process in step S26 of FIG. 4, so that the rotation speed of the compressor 10 does not decrease and the decrease in the discharge pressure stops.
After that, the compressor 10 is operated with the discharge pressure adjusted to be smaller than P1 and in the range of P2 or more.

FIG. 5B is a diagram showing a time change of the suction superheat degree of the compressor 10 with the horizontal axis as the operating time and the vertical axis as the superheat degree.
Similar to the description of FIG. 5A, the suction superheat degree increases in conjunction with the discharge pressure of the compressor 10 with the lapse of the operation time.

As described with reference to FIG. 5A, when the discharge pressure reaches P1, the control unit 30a reduces the rotational speed of the compressor 10 by step S21 of FIG. At this time, since the control unit 30a opens the valve opening degree of the outdoor expansion valve in step S23 of FIG. 4, the refrigerant flow rate increases and sucks as shown in FIG. 5B in synchronization with the pressure drop in FIG. 5A. The degree of overheating decreases.

When the suction superheat degree drops to T2, the control unit 30a closes the valve opening degree of the outdoor expansion valve in step S25 of FIG. 4, so that the refrigerant flow rate decreases and the suction superheat degree starts to increase.
After that, the compressor 10 is operated in a state where the suction superheat degree is larger than T2 and there is no liquid return.

In the compressor 10 of the present embodiment, whether the discharge superheat degree or the suction superheat degree of the compressor 10 is equal to or less than a predetermined value while the rotation speed of the compressor 10 is reduced so that the discharge pressure is within a predetermined pressure range. Whether or not the liquid has returned to the compressor 10 is determined depending on whether or not the liquid has returned, and when it is determined that the liquid has returned, the valve opening degree of the outdoor expansion valve 13 is closed, so that the liquid compression of the compressor 10 can be suppressed.

Further, the present invention is not limited to the above-described embodiment, and includes various modifications. The above-mentioned examples have been described in detail for the sake of easy understanding in the present invention, and are not necessarily limited to those having all the configurations described. Further, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment.

10 Compressor 11 Four-way valve 12 Indoor heat exchanger 13 Outdoor expansion valve 14 Outdoor heat exchanger 15 Accumulator 16 Tank 20 Suction temperature sensor T
21 Inhalation pressure sensor P
22 Discharge temperature sensor T
23 Discharge pressure sensor P
30 Outdoor unit control device 30a Control unit 30b Storage unit 31 Indoor unit control device 40 Gas connection piping 41 Liquid connection piping 100 Air conditioner Fi Indoor fan Fo Outdoor fan Gi Gas side of indoor heat exchanger 12 Li Indoor heat exchanger 12 Liquid side Go Gas side of outdoor heat exchanger 14 Lo Liquid side of outdoor heat exchanger 14 Hi Indoor unit Ho Outdoor unit V1 Gas side blocking valve V2 Liquid side blocking valve

Claims (7)

Equipped with a control unit that controls the refrigeration cycle of the air conditioner
The control unit
It is determined whether or not the discharge pressure of the compressor is equal to or higher than the predetermined pressure control value.
When the discharge pressure is equal to or higher than the predetermined pressure control value, the rotation speed of the compressor is reduced to reduce the amount of refrigerant flowing into the heat exchanger serving as the condenser, and the valve opening of the outdoor expansion valve is increased. The pressure is increased, and the refrigerant accumulated in the heat exchanger serving as the condenser is discharged from the heat exchanger.
An air conditioner characterized in that the valve opening degree of the outdoor expansion valve, which has been increased, is reduced when the discharge superheat degree or the suction superheat degree of the compressor of the compressor is equal to or less than a predetermined value. An air conditioner that harmonizes air by the refrigeration cycle of the refrigerant.
Discharge pressure detecting means for detecting the discharge pressure of the refrigerant of the compressor, and
An outdoor expansion valve that reduces the pressure of the refrigerant,
The condenser is controlled by reducing the rotation speed of the compressor and increasing the valve opening degree of the outdoor expansion valve so that the discharge pressure detected by the discharge pressure detecting means has a pressure value within a predetermined range. While reducing the amount of refrigerant flowing into the heat exchanger, the refrigerant accumulated in the heat exchanger is discharged from the heat exchanger, and during that time, it is determined whether or not the liquid has returned to the compressor, and the liquid is liquid. An air conditioner provided with a control unit that reduces the valve opening degree of the outdoor expansion valve that has been increased in response to a decrease in the rotation speed of the compressor when it is determined that there is a return. .. In the air conditioner according to claim 2,
The control unit calculates the discharge superheat degree of the refrigerant by subtracting the saturation temperature corresponding to the discharge pressure of the refrigerant from the temperature of the discharge refrigerant of the compressor, and when the discharge superheat degree is equal to or less than a predetermined threshold value, the compressor is sent to the compressor. An air conditioner characterized by determining that the liquid return is present. In the air conditioner according to claim 2,
The control unit calculates the suction superheat degree of the refrigerant by subtracting the saturation temperature corresponding to the suction pressure of the refrigerant from the temperature of the suction refrigerant of the compressor, and when the suction superheat degree is equal to or less than a predetermined threshold value, the compressor is sent to the compressor. An air conditioner characterized by determining that there is a liquid return. In the air conditioner according to claim 4,
The control unit is an air conditioner characterized in that the pressure estimated from the evaporation temperature on the evaporator side is used as the suction pressure of the refrigerant. In the air conditioner according to any one of claims 2 to 5.
The discharge pressure detecting means is an air conditioner characterized in that the pressure estimated from the condensation temperature of the condenser is used as the discharge pressure. In the air conditioner according to any one of claims 2 to 5.
The discharge pressure detecting means is an air conditioner characterized by being a pressure breaking device that operates at a pressure value within the predetermined range.

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