Patent ID: 8020394

Claim:
An air conditioner comprising: an outdoor unit having an outdoor heat exchanger for heat exchange between outdoor air and a refrigerant, and a compressor for compressing the refrigerant; at least one indoor unit, each indoor unit having an indoor heat exchanger for heat exchange between indoor air and the refrigerant; at least one refrigerant pipe, each refrigerant pipe corresponding to a single indoor heat exchanger of an indoor unit, and connecting the outdoor heat exchanger to the corresponding indoor heat exchanger; an expansion valve provided on each refrigerant pipe for the expansion of the refrigerant; a temperature sensor provided on each refrigerant pipe; a pressure sensor provided at the compressor; and a control device configured to: determine an operating condition of the air conditioner by comparing data gauged at the pressure and temperature sensors with data representative of threshold air conditioner operating conditions, select an operation mode of the air conditioner on the basis of the determination, the operation modes including a cooling/heating mode to cool and heat indoor air, an oil recovery mode to recover oil circulated during other operation modes, and a defrost mode to remove frost generated during other operation modes, and control the opening speed of the expansion valves according to the selected operation mode, the opening speed of the expansion valves when the cooling/heating operation mode is selected being faster than the opening speed of the expansion valves when the oil recovery operation mode or the defrost operation mode is selected, wherein, when the oil recovery operation mode is selected, the control device operates the air conditioner to recover oil into the compressor, changing the operation capacity of the compressor.