An air conditioner comprising: an indoor unit including an indoor unit controller, a display, an indoor fan, an indoor heat exchanger, and an indoor heat exchanger temperature detector configured to detect inlet temperature of the inlet refrigerant pipe of the indoor heat exchanger; an outdoor unit connected to the indoor unit by at least one refrigerant pipe, and including an outdoor unit controller, a compressor and an outdoor unit power supply device configured to receive power to be used in the outdoor unit, wherein the indoor unit and the outdoor unit are configured to form a refrigeration cycle; a storage device configured to store data generated during operation of the air conditioner and software to operate the air conditioner; and a controller (202, 210, 212, 214, 252, 260) comprising the outdoor unit controller and the indoor unit controller and configured to perform a test run including a first test run and a second test run to diagnose whether the air conditioner is properly installed; wherein the controller (202, 210, 212, 214, 252, 260) is configured to: perform the first test run to operate the indoor fan; perform the second test run to operate the compressor for a predetermined time, tn2; determine whether a valve is clogged based on a result of the first test run and a result of the second test run, wherein the controller (202, 210, 212, 214, 252, 260) is configured to determine that the valve is clogged if a difference between a first inlet temperature (Teva_in) of the indoor heat exchanger detected by the indoor heat exchanger temperature detector before the compressor is operated and a second inlet temperature (Teva_in+1) of the indoor heat exchanger detected by the indoor heat exchanger temperature detector after the compressor is operated is less than a first reference value, Ta, if the controller (202, 210, 212, 214, 252, 260) determines that the valve is clogged, the controller (202, 210, 212, 214, 252, 260) is configured to stop operating the compressor and the indoor fan and to display an error on the display. an indoor unit including an indoor unit controller, a display, an indoor fan, an indoor heat exchanger, and an indoor heat exchanger temperature detector configured to detect inlet temperature of the inlet refrigerant pipe of the indoor heat exchanger; an outdoor unit connected to the indoor unit by at least one refrigerant pipe, and including an outdoor unit controller, a compressor and an outdoor unit power supply device configured to receive power to be used in the outdoor unit, wherein the indoor unit and the outdoor unit are configured to form a refrigeration cycle; a storage device configured to store data generated during operation of the air conditioner and software to operate the air conditioner; and a controller (202, 210, 212, 214, 252, 260) comprising the outdoor unit controller and the indoor unit controller and configured to perform a test run including a first test run and a second test run to diagnose whether the air conditioner is properly installed; wherein the controller (202, 210, 212, 214, 252, 260) is configured to: perform the first test run to operate the indoor fan; perform the second test run to operate the compressor for a predetermined time, tn2; determine whether a valve is clogged based on a result of the first test run and a result of the second test run, perform the first test run to operate the indoor fan; perform the second test run to operate the compressor for a predetermined time, tn2; determine whether a valve is clogged based on a result of the first test run and a result of the second test run, wherein the controller (202, 210, 212, 214, 252, 260) is configured to determine that the valve is clogged if a difference between a first inlet temperature (Teva_in) of the indoor heat exchanger detected by the indoor heat exchanger temperature detector before the compressor is operated and a second inlet temperature (Teva_in+1) of the indoor heat exchanger detected by the indoor heat exchanger temperature detector after the compressor is operated is less than a first reference value, Ta, if the controller (202, 210, 212, 214, 252, 260) determines that the valve is clogged, the controller (202, 210, 212, 214, 252, 260) is configured to stop operating the compressor and the indoor fan and to display an error on the display.