Air-conditioning apparatus

An air-conditioning apparatus having a refrigeration cycle in which a compressor, a refrigerant flow switching device, a heat source side heat exchanger, a use side expansion device, and a use side heat exchanger are connected to one another using a refrigerant pipe, the air-conditioning apparatus comprising:

• an injection pipe having one side connected to an injection port of the compressor, and the other side connected to the refrigerant pipe between the use side expansion device and the heat source side heat exchanger, the injection pipe being configured to inject a refrigerant during a compression operation of the compressor;
• a refrigerant heat exchanger configured to exchange heat between the refrigerant, upon flowing through the refrigerant pipe in the refrigeration cycle, and the refrigerant, upon flowing through the injection pipe;
• a connecting pipe having one side connected to a refrigerant pipe between the refrigerant flow switching device and the use side heat exchanger, and the other side connected to the injection pipe, the connecting pipe being configured to guide a part of the refrigerant, as discharged from the compressor, to the heat source side heat exchanger and then to cause the part of the discharged refrigerant to flow into the injection pipe, wherein
• in a case of a heating operation in which the use side heat exchanger functions as a condenser when outside air has a predetermined low temperature,
• a low-outside-air-temperature heating operation start mode is executed in which, while the refrigerant, as discharged from the 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.