In the case of a heating operation in which a use side heat exchanger functions as a condenser when the outside air has a predetermined low temperature, a low-outside-air-temperature heating operation start mode is executed in which, while a refrigerant, as discharged from a compressor, flows into the use side heat exchanger, the refrigerant, upon flowing into the injection pipe, merges with a part of the refrigerant discharged from the compressor, which has traveled through the connecting pipe and has transferred heat in the heat source side heat exchanger, and a merged refrigerant is supplied to the injection port of the compressor, and thereafter a low-outside-air-temperature heating operation mode is executed in which the refrigerant, as discharged from the compressor, is supplied to the injection port of the compressor via the injection pipe while flowing into the use side heat exchanger.

An air-conditioner including a main refrigerant circuit having a compressor, a heat-source-side heat exchanger, an expansion valve, and a utilization-side heat exchanger, a bypass path, another expansion valve that decompresses refrigerant flowing in the bypass path, an internal heat exchanger, an opening degree adjuster, and a setter that sets the target temperature difference on the basis of the degree of subcooling of the utilization-side heat exchanger.

An air conditioner including a compressor including a discharge side; an outdoor heat exchanger configured to exchange heat with outdoor air; a base arranged to support the compressor and the outdoor heat exchanger; a four-way valve arranged between the discharge side of the compressor and the outdoor heat exchanger; a defrost pipe arranged at the base and configured to receive refrigerant discharged from the compressor to supply heat of the refrigerant discharged from the compressor to the base; and a defrost valve arranged on the defrost pipe and configured to adjust a flow rate of the refrigerant flowing through the defrost pipe.