LG Air Conditioner Error Code E128

E128 indicates a self-diagnostic error related to the evaporator pipe temperature sensor, detected during LG's try-run mode routine. The unit runs this self-check at startup to confirm all sensors are reading within expected ranges. When the evaporator pipe sensor signal falls outside acceptable parameters, the system logs E128 and stops operation. The fault can involve the sensor itself, its wiring, or its connectors.

No, you should not attempt to run the unit while E128 is active. The error indicates the evaporator pipe sensor is not reporting correctly, which means the control board cannot properly regulate refrigerant conditions. Operating without accurate sensor feedback can lead to compressor damage or evaporator freeze-up. The unit should remain off until the fault is diagnosed and repaired.

Repair costs vary depending on the root cause. If only a connector needs reseating, the cost may be limited to a service call fee, typically in the range of $75 to $150. Replacing the evaporator pipe thermistor is generally an affordable repair, with parts and labor often ranging from $100 to $250. If the indoor control PCB is the cause, expect higher costs, often in the $250 to $600 range depending on the model and labor rates in your area.

Some basic checks are within reach for a knowledgeable DIYer, such as inspecting sensor connectors for looseness and confirming the thermistor is properly clipped to the evaporator pipe. However, testing sensor resistance values and diagnosing wiring faults requires a multimeter and familiarity with reading technical data for the unit. If the sensor or PCB needs replacement, a qualified HVAC technician should perform the work, as accessing the evaporator section involves handling refrigerant-side components.

A power reset may temporarily clear the displayed code, but if the underlying sensor fault is still present, E128 will return when the unit runs its try-run self-diagnostic again at the next startup. A reset is not a repair. The sensor circuit needs to be properly inspected and the root cause corrected before the error will stay cleared.