LG Air Conditioner Error Code E366

E366 indicates that the second inverter control board (PBA2) has detected either an over-voltage or low-voltage condition on its power supply input. This error is specific to three-phase systems operating on a 380V supply connected at the R, S, and T terminal blocks. The board's internal protection circuit shuts the unit down to prevent damage to the inverter and compressor. The first step is to power off the unit and verify correct voltage at all three terminal blocks.

No, you should not attempt to operate the unit while E366 is active. The error indicates a voltage condition that is outside safe operating limits for the inverter board and compressor. Continuing to run the unit could cause serious damage to the inverter PBA2, the compressor, or both. Power the system off and have a technician inspect the electrical supply before restarting.

Repair costs vary depending on the root cause. If the issue is a loose terminal connection or an upstream wiring problem, the repair may cost relatively little, typically in the range of a standard service call fee. If the inverter PBA2 board itself has failed and needs replacement, parts and labor costs can range from several hundred to over a thousand dollars depending on the model and part availability. A technician will need to diagnose the supply voltage first before an accurate estimate can be given.

Diagnosing E366 requires measuring three-phase 380V supply voltage, which is hazardous and should only be performed by a qualified electrician or HVAC technician. A technician can check terminal connections and measure incoming voltage to determine whether the issue is with the building's electrical supply or the inverter board itself. If the board has failed, it must be replaced by a professional. This is not a DIY repair.

A power reset may temporarily clear the fault display, but the error will return if the underlying voltage problem has not been corrected. Simply resetting the unit without addressing the supply voltage or wiring issue does not fix the root cause. The system needs to be inspected and the voltage at the R, S, and T terminals confirmed to be within normal range before the error will stay cleared.