LG Air Conditioner Error Code 39

Error code 39 indicates a transmission error between the PFC Micom and the INV Micom on the outdoor unit's inverter PCB. These are two microcontrollers on the same board that must communicate to coordinate compressor and power factor correction operation. When that internal communication fails, the system shuts down and displays this code. A software version mismatch or a faulty inverter PCB are the most common causes.

A power reset may temporarily clear the error if the communication failure was caused by a transient condition such as a voltage fluctuation. However, if the root cause is a firmware mismatch or a damaged inverter PCB, the error will return shortly after the unit attempts to restart. A reset alone is not a repair for this fault.

If the issue is a firmware version mismatch that can be corrected without parts, you would pay only for a service call and diagnostic time. If the inverter PCB assembly requires replacement, total repair costs including parts and labor typically range from a few hundred dollars to over a thousand dollars, depending on the unit model and local labor rates. Getting a diagnosis from a qualified technician before authorizing parts replacement is advisable.

Basic checks such as power cycling the unit or verifying that nothing has physically disturbed the outdoor unit are reasonable first steps. However, resolving error 39 typically requires checking firmware version compatibility on the inverter PCB or replacing the board, both of which involve working inside a high-voltage outdoor unit. This work is best performed by a qualified HVAC technician.

No. Error 39 causes the system to shut down the compressor because reliable communication between the two inverter control processors cannot be confirmed. Attempting to force the unit to run in this condition could result in uncontrolled inverter operation and potential damage to the compressor or other components. The unit should remain off until the fault is diagnosed and corrected.