Air conditioner

1. An air conditioner comprising:

an indoor unit having an indoor heat exchanger installed therein;

a first outdoor unit having a first outdoor heat exchanger and a first compressor installed therein;

a second outdoor unit having a second outdoor heat exchanger and a second compressor installed therein;

an auxiliary module configured to connect the indoor unit, the first outdoor unit, and the second outdoor unit to each other;

a first connection line to which the auxiliary module and the first outdoor unit are connected;

a second connection line to which the auxiliary module and the second outdoor unit are connected; and

a two-stage compression line configured to connect the first outdoor unit and the second outdoor unit to each other,

wherein the two-stage compression line includes:

a first two-stage compression line configured to allow a refrigerant that exchanges heat by the second outdoor heat exchanger to flow to the first outdoor unit; and

a second two-stage compression line configured to allow a refrigerant compressed by the first compressor to flow to the second outdoor unit,

wherein the first connection line includes a first heat exchanger input and output line to which the auxiliary module and the first outdoor heat exchanger are connected,

wherein the auxiliary module further includes an auxiliary module injection line configured to connect the first heat exchanger input and output line and the second two-stage compression line to each other, and

wherein the auxiliary module injection line includes installed therein:

an auxiliary module injection expansion valve configured to expand a refrigerant flowing in the auxiliary module injection line from the first heat exchanger input and output line; and

an auxiliary module injection heat exchanger configured to exchange heat between a transmitted through the auxiliary module injection expansion valve and a refrigerant flowing in the first heat exchanger input and output line.

2. The air conditioner of claim 1 , wherein the auxiliary module includes an auxiliary module valve installed to open the first connection line and to allow a refrigerant to flow to the indoor unit through the first connection line and the second connection line in a one-stage heating mode, and to close the first connection line and to allow the refrigerant to the indoor unit through only the second connection line in a two-stage heating mode.

3. The air conditioner of claim 2 , wherein the refrigerant flowing in the first connection line and the second connection line is compressed by the first compressor and the second compressor, respectively, and flows to the auxiliary module along the first connection line and the second connection line, in the one-stage heating mode; and

wherein the refrigerant flowing in the first connection line and the second connection line is compressed by the first compressor and the second compressor, sequentially, and flows to the auxiliary module along the second connection line, in the two-stage heating mode.

4. The air conditioner of claim 1 , wherein the first outdoor unit includes a first main four-way valve and a first auxiliary four-way valve;

wherein the second outdoor unit includes a second main four-way valve and a second auxiliary four-way valve; and

wherein, when a one-stage heating mode and a two-stage heating mode are switched with each other, any one of the first main four-way valve and the first auxiliary four-way valve, and any one of the second main four-way valve and the second auxiliary four-way valve are configured to reverse the flow therethrough.

5. The air conditioner of claim 4 , wherein the first auxiliary four-way valve is disposed to allow a refrigerant transmitted through the first compressor to flow to the indoor unit, in the one-stage heating mode; and

wherein the first auxiliary four-way valve is disposed to allow a refrigerant transmitted through the first compressor to flow to the second outdoor unit, in the two-stage heating mode.

6. The air conditioner of claim 4 , wherein the second main four-way valve is disposed to allow a refrigerant transmitted through the second outdoor heat exchanger to flow to the second compressor, in the one-stage heating mode; and

wherein the second main four-way valve is disposed to allow a refrigerant transmitted through the second outdoor heat exchanger to flow to the first outdoor unit, in the two-stage heating mode.

7. The air conditioner of claim 1 , wherein the second two-stage compression line penetrates the auxiliary module and extends to the second outdoor unit.