LG Air Conditioner Error Code 205

Error code 205 on an LG air conditioner indicates a communication error between the HR (Heat Recovery) unit and the upgraded RS-485 modem in a 4-series system. The two components have lost their data link and the system cannot operate normally as a result. A red LED on the 485 modem module is typically illuminated when this fault is active. Diagnosing the fault starts with inspecting the communication wiring and checking the modem LED status.

Error code 205 is a communication fault, not a safety-critical failure involving refrigerant, electrical hazards, or fire risk. The system shuts down operation when this error occurs specifically to prevent uncontrolled behavior, which is a protective response. While the error itself is not dangerous, a non-functional HVAC system in extreme temperatures can become uncomfortable or problematic, so timely diagnosis is recommended.

A power reset may temporarily clear the error code display, but if the underlying communication fault between the HR unit and the 485 modem has not been corrected, the error 205 will return once the system restarts and attempts to re-establish communication. A reset alone is not a repair and should only be used as part of the diagnostic process after addressing the identified fault.

Some causes of error 205, such as a loose terminal connection on the communication wiring, can be addressed by a knowledgeable DIYer who is comfortable working with low-voltage control wiring. However, correctly diagnosing RS-485 communication faults, checking signal integrity, and replacing modem modules or control boards typically requires specialized knowledge and tools. For most homeowners, calling a qualified HVAC technician is the safest and most efficient approach.

Repair costs vary depending on the root cause. If the fix is simply reseating or replacing a damaged communication cable, costs may fall in the range of $75 to $200 including labor. If the upgraded 485 modem module requires replacement, parts and labor costs typically range from $200 to $600 or more depending on the specific component and local labor rates. HR unit control board replacement would be at the higher end of the repair cost spectrum.