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.

An air conditioner including a hot gas line for receiving a portion of refrigerant compressed in a compressor, an indoor heat exchanger, an outdoor expansion device for expanding the refrigerant having exchanged heat in the indoor heat exchanger, an outdoor heat exchanger functioning as a condenser in a cooling mode while functioning as an evaporator in a heating mode, and a 4-way valve for receiving a remaining portion of the compressed refrigerant, to guide the refrigerant emerging from the compressor to the outdoor heat exchanger in the cooling mode and to the indoor heat exchanger in the heating mode. The outdoor heat exchanger includes a main heat exchanger section functioning as a condenser in the cooling mode while functioning as an evaporator in the heating mode, and an auxiliary heat exchanger for receiving the refrigerant from the hot gas line in a frosting prevention mode.

An air-conditioning apparatus includes: a first defrosting pipe branching from a main circuit to supply a portion of refrigerant discharged from a compressor to one of plural parallel heat exchangers to be defrosted; a second defrosting pipe which returns, to the main circuit, the refrigerant supplied through the first defrosting pipe to the one parallel heat exchanger; a first expansion device provided on the first defrosting pipe; a second expansion device provided on the second defrosting pipe to adjust a pressure of the refrigerant in the one parallel heat exchanger; and a third expansion device provided between a connection point between an outlet of the second defrosting pipe and the main circuit and one of plural indoor heat exchangers functioning as an evaporator, to adjust a pressure of the refrigerant in the one of the indoor heat exchangers; and a controller that controls the second and third expansion devices individually.

In plural heat-source-side heat exchangers included in an outdoor unit of an air-conditioning apparatus, bypasses for defrosting are provided with flow-rate adjusting mechanisms for refrigerant flowing into the bypasses. The flow rates of the refrigerant which are to be adjusted by the flow-rate adjusting mechanisms are determined in accordance with ambient environments of plural heat-source-side heat exchangers.

An air-conditioning apparatus includes a refrigerant circuit and a controller. The refrigerant circuit includes a main circuit and a bypass circuit. The bypass circuit is connected, by a pipe, to each of a plurality of parallel outdoor heat exchangers via a defrosting refrigerant pressure-reducing device, a defrosting flow passage switching device, and a backflow prevention device. The controller switches a flow passage for use in introduction of refrigerant using the defrosting flow passage switching device, to select one of the plurality of parallel outdoor heat exchangers as a defrosting target to be defrosted; and supplies defrosting refrigerant whose pressure is reduced by the defrosting refrigerant pressure-reducing device to the selected one of the plurality of parallel outdoor heat exchangers.

Even in the case of a large outdoor heat exchanger (24), it is possible to completely remove frost without reducing the defrosting effect. Provided are: a distributor (25) installed between the outdoor heat exchanger (24) and an expansion valve (26); a plurality of distribution pipes (252) of which one end is connected to the distributor (25) and of which the other end is connected to a plurality of heat transfer pipes (241) of the outdoor heat exchanger (24); and a bypass pipe (30) of which one end is connected to a compressor (23) and diverges on the way, and simultaneously of which the respective plurality of other ends are connected to a connection part between the distribution pipe (252) and the heat transfer pipe (241) or in the vicinity thereof.