Air-conditioning apparatus with pressure control for defrosting and heating

An air-conditioning apparatus comprising:

• heat-source-side units each including a compressor and a heat-source-side heat exchanger;
• a load-side unit including a load-side heat exchanger and a load-side expansion device;
• a first header connecting a refrigerant pipe connected to the load-side heat exchanger and connecting refrigerant pipes each connected to a corresponding one of the compressors;
• a second header connecting a refrigerant pipe connected to the load-side expansion device and connecting refrigerant pipes each connected to a corresponding one of the heat-source-side heat exchangers;
• bypass expansion devices each provided between the second header and a corresponding one of the heat-source-side heat exchangers;
• circuit switchers each provided in a corresponding one of the heat-source-side units and each circuit switcher is configured to connect the heat-source-side heat exchanger to a suction portion of the compressor when the heat-source-side heat exchanger functions as an evaporator and connect the heat-source-side heat exchanger to a discharge portion of the compressor when the heat-source-side heat exchanger is defrosted;
• a connection pipe connecting, to each other, the suction portions of the compressors that are provided in the heat-source-side units respectively;
• discharge pressure sensors each provided to the discharge portion of a corresponding one of the compressors;
• bypass pressure sensors each provided between the second header and a corresponding one of the bypass expansion devices;
• and
• a controller configured to cause the heat-source-side heat exchanger in at least one of the heat-source-side units to be defrosted and cause the heat-source-side heat exchanger of at least one remaining heat-source-side unit of the heat-source-side units to act as an evaporator,
• the controller
• being configured to control the circuit switcher in the at least one of the heat-source-side units in such a manner that a portion of refrigerant discharged from a corresponding one of the compressors flows into a corresponding one of the heat-source-side heat exchangers, and
• being configured to control an opening degree of the bypass expansion device in the at least one of the heat-source-side units in such a manner that a value representing a difference between pressure measured by a corresponding one of the discharge pressure sensors and pressure measured by a corresponding one of the bypass pressure sensors is equal to or greater than a predetermined value.