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, an expansion valve, a flow switching device, a heat source side heat exchanger including a first heat source side heat exchanger and a second heat source side heat exchanger connected in parallel, an opening-and-closing valve provided on downstream of the second heat source side heat exchanger through which refrigerant flows during a defrosting operation, and a controller that, when the defrosting operation is performed, controls the flow switching device so that the refrigerant discharged from the compressor flows into the heat source side heat exchanger. The controller switches the opening-and-closing valve from an open state to a closed state when the defrosting operation is started, determines a point in time when defrosting targets to be defrosted are switched, and switches the opening-and-closing valve from the closed state to the open state in accordance with the point in time determined.

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 refrigerating cycle apparatus is equipped with a plurality of outdoor units, each of which includes at least one high-pressure type compressor with refrigerant and lubricating oil stored therein. A discharge pipe of the respective compressor is connected to a main discharge pipe for jointly discharging refrigerant and oil to the indoor unit. A suction pipe of the respective compressors is connected for returning the refrigerant and the oil from the indoor unit to the compressor. Each outdoor unit comprises a first oil balancing circuit connected between a side surface of the casing of the respective compressor and the main discharge pipe for allowing a flowing-in of the exceeding oil from the casing of the compressor. In another embodiment, each outdoor unit may include a second oil balancing circuit connected between a side surface of the casing of the respective compressor and the main suction pipe.

An outdoor unit according to the present disclosure includes: a compressor that sucks refrigerant, compresses the sucked refrigerant, and discharges the compressed refrigerant; a first refrigerant flow switching device that switches a flow passage for the refrigerant between a flow passage for a cooling operation and a flow passage for a heating operation; a heat-source-side heat exchanger that causes heat exchange to be performed between the refrigerant and external fluid; a heat-source-side backflow prevention device and a connection pipe that are included in a flow passage for the refrigerant in which an outlet from which the refrigerant flows to an outside region and an inlet into which the refrigerant flows from the outside region are unchanged regardless of which of the cooling operation and the heating operation is performed; and a flow passage pipe through which part of the refrigerant having flowed from the inlet passes in the cooling operation.

An air conditioner includes an ejector that raises a pressure of refrigerant by using energy for refrigerant decompression and expansion. A switching mechanism switches between a refrigerant flow in a first operation and a refrigerant flow in a second operation. The air conditioner is configured such that in the first operation, refrigerant compressed by a compression mechanism radiates heat in a use-side heat exchanger and is decompressed and expanded by the ejector while refrigerant evaporated in a heat-source-side heat exchanger is raised in pressure by the ejector. The air conditioner is configured such that in the second operation, refrigerant compressed by the compression mechanism radiates heat in the heat-source-side heat exchanger and is decompressed and expanded by a first expansion valve before being evaporated in the use-side heat exchanger while refrigerant does not flow through the ejector.

A thermo-hygrostat air conditioner is provided that may include at least one indoor unit installed indoors, and including a main coil that provides air that meets a predetermined humidity by dehumidifying outdoor air and a sub coil that cools or heats the dehumidified air at a predetermined temperature and provides the air indoors; and an outdoor unit connected to the main coil and the sub coil of the indoor unit via a refrigerant pipe and including at least one outdoor heat exchanger, at least one compressor, at least one outdoor expansion valve and at least one four way valve. A mode of the main coil and the sub coil may be determined depending on a cooling load and a heating load. The outdoor unit may control the four way valve according to the mode of the main coil and the sub coil and provide refrigerant to the main coil and the sub coil according to the mode.

A heat pump system includes a first unit; a second unit connected to a first flow path of the first unit; and a third unit connected to a second flow path of the first unit and connected to the second unit. The heat pump system can operate in a cooling and water heating mode and a heating and water heating mode, wherein, in the cooling and water heating mode, the heat pump system is configured to switch a switching assembly to a first position and connect the at least one first heat exchangers and the second heat exchanger in series; in the heating and water heating mode, the heat pump system is configured to switch the switching assembly to a second position and connect the second heat exchanger and the at least one third heat exchangers in parallel.

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 $R=\left({\rho }_{\mathrm{md}}\times V_{\mathrm{md}}\times A_d\right)\text{/}(C_r\times {\left(2\times \Delta P_r\text{/}{\rho }_{1\mathrm{rl}}\right)}^{0.5}\times A_v\times {\rho }_{1\mathrm{rl}}+A_v$

An air-conditioning apparatus includes a main circuit in which a compressor, a flow switching device, an indoor heat exchanger, a pressure reducing device, and a plurality of parallel heat exchangers connected in parallel with each other are connected by pipes, a bypass pipe, a flow control device provided to the bypass pipe and configured to adjust a flow rate of refrigerant flowing through the bypass pipe, an evaporating pressure sensor configured to measure an evaporating pressure of the refrigerant, and a controller. The air-conditioning apparatus is configured to operate in a normal heating operation mode and a heating-defrosting operation mode. When an operation associated with the normal heating operation mode is switched to an operation associated with the heating-defrosting operation mode, the controller adjusts an opening degree of the flow control device using the evaporating pressure in the parallel heat exchanger and a driving frequency of the compressor.