LG Air Conditioner Error Code E504

E504 means the LG air conditioner's control board ran a self-diagnosis on the compressor and detected an abnormal condition. The unit shuts down to protect the compressor from running under a fault state. The underlying problem could be the compressor itself, the inverter board that drives it, the start capacitor, or an inadequate power supply.

No. When E504 is active, the LG unit disables compressor operation, so the system will not cool or heat. Attempting to force the unit to run through an active compressor fault risks burning out the compressor windings or causing irreversible damage to the inverter board. Leave the unit off and address the fault before resuming operation.

A power reset may temporarily clear the display, but E504 will return as soon as the control board runs the compressor self-diagnosis again if the underlying fault still exists. A reset is useful only as a first step to confirm the fault is repeatable, not as a fix. Do not assume the problem is resolved just because the code disappears briefly after cycling power.

Start by checking the supply voltage at the disconnect to confirm the unit is receiving stable power within its rated range. Next, on non-inverter models, test the compressor start capacitor with a multimeter and replace it if capacitance is out of spec. If voltage and the capacitor are good, the inverter board or compressor motor itself needs to be tested. Inverter board and compressor diagnosis and replacement should be handled by a certified HVAC technician, as it involves high-voltage components and refrigerant handling.

Cost depends on the failed component. A start capacitor typically costs $10 to $30 for the part plus one hour of labor. An inverter drive board runs $150 to $400 depending on the model. A compressor replacement is the most expensive scenario, often ranging from $600 to $1,500 or more including labor and refrigerant, and on older units this cost may approach or exceed the value of the equipment.