LG Air Conditioner Error Code E321

E321 indicates a short or open circuit fault in the EVI In temperature sensor, which monitors refrigerant temperature at the inlet of the Enhanced Vapor Injection circuit. The control board is receiving a resistance reading outside the valid range, meaning it cannot obtain an accurate temperature measurement. The system shuts down to prevent operating with incorrect refrigerant injection parameters.

The unit will generally prevent normal operation when E321 is active, which is a protective measure. Attempting to bypass or ignore this fault and force the system to run without a valid EVI sensor reading could result in improper refrigerant injection and potential compressor damage. It is best to leave the unit off until the sensor fault is diagnosed and corrected.

Repair costs vary depending on the root cause. If only the sensor needs replacement, parts and labor typically fall in the range of $100 to $300. If the control board is the source of the fault, costs can rise to the $300 to $600 range or higher depending on the model and labor rates in your area. A diagnostic visit fee may also apply before any repair estimate is provided.

A knowledgeable DIYer can begin by checking whether the sensor connector has simply come loose from the PCB and reseating it firmly. However, measuring sensor resistance, inspecting refrigerant circuit components, and replacing the EVI sensor or PCB typically require familiarity with HVAC systems and, in some regions, a refrigerant handling certification. If you are not comfortable working with these components, a qualified technician should handle the repair.

Performing a power reset may temporarily clear the error display, but E321 will return if the underlying sensor fault still exists. If the connector had simply vibrated loose, reseating it before the reset may result in a lasting fix. In all other cases, the faulty sensor, wiring, or board must be repaired or replaced before the error will clear permanently.