LG Hvac Error Code E221

The E221 error code on an LG HVAC system indicates a fault detected in the outdoor ambient temperature sensor circuit. This sensor, sometimes called the outdoor air thermistor, monitors the external air temperature and feeds that data to the control PCB so the system can optimize compressor operation, defrost cycles, and capacity adjustments. When the control board detects a signal that falls outside the expected resistance range for the sensor, it classifies the fault as either a short circuit (resistance too low) or an open circuit (resistance too high or no signal), and triggers E221 to halt or limit operation.

The sensor connects to the outdoor unit's main PCB through a dedicated connector labeled CN41. A loose, corroded, or fully dislodged connector at this point is the most common trigger for this fault, since even a partial loss of contact can produce a signal that mimics a failed sensor. Beyond the connector, the thermistor itself can fail due to moisture intrusion, physical damage from debris, or age-related drift in its resistance characteristics. Wiring between the sensor and the PCB can also develop faults from rodent damage, vibration fatigue, or corrosion at crimp points.

Diagnosing E221 requires starting at connector CN41 on the PCB to confirm it is fully seated and free of corrosion or bent pins. If the connector is secure, the next step is measuring the thermistor resistance directly across its leads and comparing that value to the temperature-to-resistance chart for the specific sensor. A reading of zero ohms indicates a short, while an infinite resistance reading confirms an open circuit. Either condition points to sensor replacement. If resistance reads within spec, the fault may lie in the wiring harness or the PCB input circuit itself.