LG Air Conditioner Error Code 104

Error code 104 on an LG air conditioner indicates a communication failure between the main outdoor unit PCB and the Sub1 outdoor unit. The main PCB is not receiving the expected data signal from Sub1. This error is specific to multi-outdoor-unit system configurations and typically requires inspection of the inter-unit communication wiring and control boards.

A power reset may temporarily clear the fault display, but if the underlying communication problem persists, the error will return. The reset is actually a useful diagnostic step: monitoring the third value in the 7-segment sequence during startup will show whether the main PCB is detecting Sub1 after the reset. A persistent low connecting count confirms the fault has not resolved.

Repair costs vary depending on the cause. If the fix involves reseating loose communication cable terminals, the cost is primarily a service call fee, typically in the range of $75 to $150. If a control board needs replacement, parts and labor combined can range from $300 to $700 or more depending on the specific PCB required and local labor rates. Getting a diagnosis before committing to parts replacement is advisable.

Some basic checks are accessible to a knowledgeable DIYer, such as visually inspecting the communication cables between outdoor units for obvious damage or loose terminal connections. However, diagnosing the 7-segment display during a power reset sequence and testing PCB communication circuits requires familiarity with the system's architecture and safe electrical practices. PCB replacement should be handled by a qualified technician.

Operating the system with error code 104 active is not recommended. The main outdoor unit cannot confirm the status of the Sub1 unit, which means the system is running without full visibility into compressor and load conditions across the outdoor units. Continuing to run the system in this state risks compressor damage or uncontrolled operating conditions. The system should be inspected before resuming normal use.