An air conditioner includes a compressor, a flow switching part, an outdoor heat exchanger including a plurality of refrigerant tubes for guiding the refrigerant heat exchanged with outdoor air, a main expansion valve disposed at one side of the outdoor heat exchanger, a first inlet/outlet tube extending from the flow switching part to the outdoor heat exchanger, and a second inlet/outlet tube extending from the outdoor heat exchanger to the main expansion valve. The outdoor heat exchanger includes a header defining a flow space for the refrigerant, the header including an upper header and a lower header, a check valve disposed between the upper header and the lower header to guide the refrigerant to flow in one direction, and a bypass tube extending from the lower header to the second inlet/outlet tube to guide a discharge of a liquid refrigerant existing in the lower header.

An outdoor unit for a multi-type air conditioner includes a compressor, a four-way valve, an outdoor heat exchanger, an outdoor expansion valve, a liquid tank, an accumulator, a shutoff valve provided for the refrigerant pipe between a liquid refrigerant inlet/outlet port and the liquid tank in the outdoor unit, and a first bypass circuit provided in the refrigerant pipe for bypassing the shutoff valve through a capillary tube to connect a liquid refrigerant inlet/outlet port side to an upper side of the refrigerant pipe in a gravity direction. The outdoor unit further includes a second bypass circuit for connecting a bottom portion of the liquid tank to an inlet side of the accumulator via an electromagnetic valve.

In an air-conditioning system, an outdoor unit and an indoor unit communicate through a relay device, including a plurality of communication ports; a plurality of communication networks having logical connection relationships with the respective communication ports; and a plurality of nodes having logical connection relationships with the respective communication networks. The plurality of nodes are each associated with one of the outdoor unit and the indoor unit. Among the plurality of nodes, a certain node is set as a first node, and another certain node different from the first node is set as a second node. The relay device executes transfer processing of transferring a communication frame from the first node to the second node, and then if the relay device does not receive a reception acknowledgment signal from the second node, limits a number of re-transmission times when the relay device re-transfers the communication frame to the second node.

In an air conditioner which is a refrigerating apparatus, a superheat degree controller is provided, which is configured to control, in an evaporation mode of an outdoor heat exchanger, the opening degree of an expansion valve such that the superheat degree of refrigerant whose flows are joined together after passing through a main heat exchange part and an auxiliary heat exchange part reaches a predetermined superheat degree. Moreover, in the air conditioner, a flow volume adjustment valve configured to adjust, in the evaporation mode of the outdoor heat exchanger, a flow ratio of refrigerant in the heat exchange parts and a flow ratio controller configured to control the flow volume adjustment valve such that refrigerant temperatures after passage through the heat exchange parts are substantially equal to each other are provided.

An air conditioner, and a control method, including a compressor to compress a refrigerant; an outdoor heat exchanger; a first four-way valve between a discharge port of the compressor and an upper inlet of the outdoor heat exchanger; a second four-way valve between the discharge port of the compressor and a lower inlet of the outdoor heat exchanger; and a controller electrically connected to the compressor and the first four-way valve and the second four-way valve to control the first and second four-way valves to perform a first defrosting operation which defrosts an upper and a lower portion of the outdoor heat exchanger during a heating operation, and control the first and second four-way valves to perform a second defrosting operation which operates the upper portion as an evaporator, and operates the lower portion as a condenser, based on a detected need for additional defrosting of the lower portion.