LG Air Conditioner Error Code 123

Error code 123 indicates that the temperature sensor on the front-side heat exchanger (A) of the sub1 outdoor unit has been detected as open or shorted. The control board cannot get a valid temperature reading from this sensor, so the system shuts down to protect itself. Diagnosis follows the CH45 procedure outlined for outdoor unit thermistor faults.

No, the system will typically prevent normal operation when error code 123 is active specifically to avoid running without accurate heat exchanger temperature data. Attempting to bypass or ignore the fault could result in compressor damage or unsafe operating conditions. The fault should be diagnosed and repaired before resuming operation.

A power reset may temporarily clear the error code from the display, but if the underlying sensor fault is still present, the code will return once the system restarts and attempts to read the thermistor. A reset does not repair a failed sensor, damaged wiring, or corroded connector. The root cause must be identified and corrected to permanently resolve the fault.

Some basic checks, such as inspecting the sensor connector for looseness or corrosion, can be done by a knowledgeable DIYer. However, testing the thermistor's resistance values and accessing the outdoor control board typically requires comfort with electrical diagnostics and disassembling the outdoor unit. If you are not experienced with HVAC electrical work, a licensed technician is the safer option.

Repair costs vary depending on what component has failed. A replacement thermistor sensor typically costs between $15 and $60 for the part alone. If a wiring harness or outdoor control board needs replacement, costs can range from $150 to $500 or more including labor. A service call for diagnosis alone generally runs between $75 and $150 depending on your region.