A refrigeration cycle apparatus includes a compressor, a four-way valve, a second flow path switching unit, a first outdoor heat exchanger, a second outdoor heat exchanger, a first indoor heat exchanger and a second flow path switching unit. The second flow path switching unit switches between a third state in which the first port, the second port, the first outdoor heat exchanger, the fourth port, the third port, the second heat exchanger, the fifth port and the sixth port are successively connected in series, and a fourth state in which the sixth port, the fourth port, the first heat exchanger, the second port and the first port are successively connected in series, and the sixth port, the fifth port, the second heat exchanger, the third port and the first port are successively connected in series.

A refrigeration cycle apparatus includes a compressor, a four-way valve, a second flow path switching unit, a first outdoor heat exchanger, a second outdoor heat exchanger, a first indoor heat exchanger and a second flow path switching unit. The second flow path switching unit switches between a third state in which the first port, the second port, the first outdoor heat exchanger, the fourth port, the third port, the second heat exchanger, the fifth port and the sixth port are successively connected in series, and a fourth state in which the sixth port, the fourth port, the first heat exchanger, the second port and the first port are successively connected in series, and the sixth port, the fifth port, the second heat exchanger, the third port and the first port are successively connected in series.

In an air conditioning apparatus, heat exchange is conducted between refrigerant passing through a first high-temperature-side flow path and refrigerant passing through a first low-temperature-side flow path of a cooler, and between refrigerant passing through a second high-temperature-side flow path and refrigerant passing through a second low-temperature-side flow path of the cooler. A switching device switches between first/second refrigerant circuits. In the first circuit, an inlet of the first high-temperature-side flow path is formed downstream of the first low-temperature-side flow path with respect to an outlet of the first high-temperature-side flow path, and in the second refrigerant circuit, an inlet of the second high-temperature-side flow path is formed downstream of the second low-temperature-side flow path with respect to an outlet of the second high-temperature-side flow path.

Excessive specifications of a shutoff valve leads to increase in production cost. An air conditioner configured to circulate a lower flammability refrigerant in a refrigerant circuit includes a first shutoff valve and a second shutoff valve configured to inhibit refrigerant leakage into a predetermined space. Each of the first shutoff valve and the second shutoff valve in a shutoff state has a shutoff leakage rate, as an air leakage rate in a case where fluid is air at 20° C. and a differential pressure between upstream and downstream of the valve is 1 MPa, more than 300 (cm.sup.3/min) and less than 300×R (cm.sup.3/min). R satisfies $R=\left({\rho }_{\mathrm{md}}\times V_{\mathrm{md}}\times A_d\right)\text{/}(C_r\times {\left(2\times \Delta P_r\text{/}{\rho }_{1\mathrm{rl}}\right)}^{0.5}\times A_v\times {\rho }_{1\mathrm{rl}}+A_v$

A method and device for adjusting an oil volume of a compressor of a multi-split system. The method comprises the following steps: (S1) during an operation of a multi-split system, detecting at a first pre-set time interval whether an oil volume of a compressor is insufficient; (S2) if the oil volume of the compressor is insufficient, controlling an oil volume adjusting unit to turn on for a second pre-set time and then turn off; (S3) acquiring a total turn-on time of the oil volume adjusting unit, and determining whether the total turn-on time exceeds a pre-set value; (S4) if the total turn-on time exceeds the pre-set value and it has not been detected over a continuous third pre-set time that the oil volume of the compressor is insufficient, recycling oil back to an oil storage tank by controlling a switch unit and the oil volume adjusting unit.

An air-conditioning apparatus includes a refrigeration circuit, a first shut-off device, a leakage detection device, and a controller configured to perform a refrigerant recovery operation in a case where refrigerant leakage is detected. At the time of the refrigerant recovery operation, the controller performs control to perform a first operation of recovering refrigerant from a load-side heat exchanger into an accumulator and a heat-source-side heat exchanger, and a second operation of moving refrigerant in the heat-source-side heat exchanger to the accumulator. In the first operation, the first shut-off device is closed, a flow passage switching device is brought into a first connection state, and a compressor is driven. The second operation is performed after the first operation, and in the second operation, the connection state of the flow passage switching device is switched to a second connection state in a state where the compressor is being operated.

A heat-pump using apparatus includes a refrigerant circuit and a heat medium circuit. The refrigerant circuit is capable of executing a heating operation and a cooling operation. A first expansion device is provided downstream of a reservoir, and a second expansion device is provided upstream of the reservoir, in the flow of refrigerant in the heating operation. A main circuit of the heat medium circuit includes a branching part and a joining part. An overpressure protection device is connected to a connection part which is located between a load-side heat exchanger and one of the branching part and the joining part or at the load-side heat exchanger. A refrigerant leakage detecting device is connected to the other of the branching part and the joining part, or between the other of the branching part and the joining part and the connection part, or to the connection part.

The amount of refrigerant to be charged in a refrigerant circuit of an air conditioner is set to a range defined by a lower-limit charge amount and an upper-limit charge amount. The lower-limit charge amount is a charge amount with which a refrigerant supercooling degree is 0 deg and a refrigerant quality is 0 at a refrigerant outlet side of a supercooling heat exchanger when a cooling operation is performed under an overload condition in which the refrigerant is hardly condensed in an outdoor heat exchanger that functions as a condenser. On the other hand, the upper-limit charge amount is a charge amount with which a refrigerant supercooling degree is 0 deg and a refrigerant quality is 0 at a refrigerant outlet side of the outdoor heat exchanger when the cooling operation is performed under a rated condition.

A two-pipe enhanced-vapor-injection outdoor unit and a multi-split system are provided. The two-pipe enhanced-vapor-injection outdoor unit includes: an outdoor heat exchanger and a second port; an enhanced-vapor-injection compressor, including a gas discharge port, a gas return port and an injection port; a reversing assembly, including first to fourth ends; a supercooler, including a main heat-exchange flow path and an auxiliary heat-exchange flow path communicated with each other, the main heat-exchange flow path being connected to the second port, the auxiliary heat-exchange flow path being connected to the injection port; and a throttling assembly having a first end connected to an outlet of the main heat-exchange flow path, and a second end connected to an inlet of the outdoor heat exchanger.

An air-conditioning system that performs a refrigeration cycle in a refrigerant circuit, includes: an outdoor unit; a plurality of indoor units; and a connection pipe disposed between the outdoor unit and the indoor units and that forms at least a refrigerant passage through which refrigerant in a gas-liquid two-phase state flows. The connection pipe includes: a branch portion that includes an indoor-side pipe group including indoor-side pipes that each communicates with any one of the indoor units, and diverges refrigerant flowing from the outdoor unit side; and a trap portion disposed in at least any one of the indoor-side pipes and is filled with refrigerant in a gas state.