Air conditioner and control method thereof

An air conditioner comprising:

• a multi-way valve having an input and a plurality of outputs;
• an outdoor heat exchanger coupled to an output of the plurality of outputs of the multi-way valve;
• a first compressor;
• a resistance channel disposed between an outlet of the first compressor and the input of the multi-way valve and configured to increase pressure of a refrigerant flowing from the outlet of the first compressor to the outdoor heat exchanger via the multi-way valve;
• a bypass channel coupled to the resistance channel in parallel;
• a bypass valve configured to open and close the bypass channel and so that, based on the bypass valve being opened, the refrigerant flowing from the outlet of the first compressor to the outdoor heat exchanger via the multi-way valve does not pass through the resistance channel;
• a second compressor having an outlet through which a refrigerant flows to the input of the multi-way valve and then to the outdoor heat exchanger via the multi-way valve, without the resistance channel being between the outlet of the second compressor and the input of the multi-way valve;
• a return channel having one end disposed downstream of the resistance channel and the bypass channel, downstream of the outlet of the second compressor, and upstream of the input of the multi-way valve, and another end that is branched into a first branch coupled with an inlet of the first compressor and a second branch coupled to an inlet of the second compressor;
• a first oil divider at an output of the first compressor and upstream of the resistance channel and the bypass channel;
• a second oil divider at an output of the second compressor and upstream of the input of the multi-way valve;
• a first pipe to provide oil separated by the first oil divider to the second compressor;
• and
• a second pipe to provide oil separated by the second oil divider to the first compressor,
• wherein the first compressor is controlled to be operated using the resistance channel in a cooling operation at a lower outdoor temperature than the second compressor is operated at.