LG Air Conditioner Error Code 156

Error code 156 on an LG air conditioner signals a transmission error between outdoor units in a multi-unit system. Specifically, the sub3 outdoor unit is not receiving communication signals from the main outdoor unit. The system shuts down to prevent uncoordinated operation that could cause equipment damage. The fault is most commonly found in the transmission cables or terminal connections between the units.

The system will typically halt operation when error 156 is active, which is actually a protective response. Attempting to force the system to run while sub3 is not communicating with the main outdoor unit can lead to uncoordinated compressor operation and potential equipment damage. It is best to leave the system off until the transmission fault is diagnosed and resolved.

A power reset may temporarily clear the error code, but if the underlying transmission fault between the outdoor units has not been corrected, the code will return once the system attempts to re-establish communication. A reset is useful as a first step to confirm whether the fault is intermittent, but it is not a substitute for diagnosing and repairing the actual wiring or component issue causing the communication failure.

A knowledgeable DIYer can inspect the transmission cables and terminal connections between outdoor units for obvious damage, loose wires, or corrosion. However, if the wiring appears intact and the error persists, diagnosing and replacing communication PCBs requires technical expertise and familiarity with multi-unit system wiring. In that case, a qualified HVAC technician should be called.

If the fix is simply reseating a loose cable or replacing a damaged transmission wire, costs are relatively low, typically in the range of $75 to $200 for a service call. If a communication PCB needs to be replaced in either the main or sub3 outdoor unit, repair costs can rise to the range of $300 to $700 or more depending on parts and labor. Getting a full diagnosis before authorizing repairs helps avoid unnecessary part replacements.