LG Air Conditioner Error Code E212

E212 indicates an MCU branch part setup error in which three or more indoor units on the same branch are assigned the same rotary switch address. The MCU cannot communicate properly with units that share an address, so it faults the system. Each indoor unit in a multi-zone system must have a unique address set via its physical rotary switch on the control board.

Pressing K3 to reset the MCU is the final step after correcting address conflicts, not a standalone fix. If the duplicate address settings are not resolved first, the E212 error will return immediately after reset. The underlying address configuration must be corrected before the reset will result in normal system operation.

If the problem is simply incorrect rotary switch positions, the repair may only require a service call to inspect and adjust the switches, typically in the range of $75 to $200 depending on the technician and number of units involved. If a faulty rotary switch or control board must be replaced, parts and labor costs can range from $150 to $500 or more depending on the specific board and system model.

Inspect the rotary address switch on each indoor unit connected to the affected branch and identify any units sharing the same address value. Re-adjust the duplicate switches so that every unit has a unique address. Once all corrections are made, press the K3 button on the MCU to reset the fault and allow the system to reinitialize communication with the indoor units.

E212 is a configuration fault rather than a safety-critical electrical hazard. However, with this error active, the MCU cannot reliably control the affected indoor units, which means the system will not operate as intended. The system should be corrected promptly to restore proper climate control, but the error does not typically indicate a fire or refrigerant risk.