LG Air Conditioner Error Code 172

Error code 172 on an LG air conditioner signals an outdoor voltage sensing error on the sub3 circuit, caused by an abnormal resistance value measured at the voltage sensor. The outdoor unit's control board monitors these sensing circuits to verify accurate power measurement, and when the resistance reading falls outside the expected range, it triggers this fault. The system shuts down to protect compressor and inverter components from operating under unknown voltage conditions.

No, it is not advisable to attempt to bypass or ignore error code 172. This fault indicates the outdoor unit cannot accurately monitor its incoming voltage conditions, which means the system may be operating on incorrect data that could lead to compressor or inverter damage. The unit should remain off until the fault is diagnosed and repaired.

Repair costs for error code 172 vary depending on what component has failed. Wiring or connector repairs tend to fall at the lower end of the cost range, typically between $75 and $200 including labor. Replacing the outdoor main PCB is the most expensive possibility, with parts and labor costs generally ranging from $300 to $700 or more depending on the unit model and local labor rates.

Resolving error code 172 typically requires access to the outdoor unit's internal electrical components, including the voltage sensing circuit and the main PCB. A homeowner can visually inspect accessible wiring and connectors for obvious damage or corrosion, but actual resistance measurements and component replacement require technical knowledge and proper safety precautions around high-voltage circuits. Most repairs for this error are best handled by a licensed HVAC technician.

A power reset may temporarily clear the fault display, but if the underlying cause is a failed sensing resistor, damaged wiring, or a faulty PCB, the error code 172 will return once the unit attempts to operate again. Resetting without addressing the root cause does not fix the problem and may allow further damage to occur.