Samsung Air Conditioner Error Code E321

E321 indicates an error with the EVI IN temperature sensor in the outdoor unit. The fault can be caused by a disconnected sensor connector, a broken wire in the sensor harness, or a defective thermistor. The EVI IN sensor monitors refrigerant temperature entering the vapor injection circuit, which is critical for efficient heat pump operation. The system flags this code when the sensor signal is absent or outside the acceptable range.

Operating the unit with an active E321 fault is not recommended. The EVI IN sensor provides data the control system uses to manage refrigerant flow through the vapor injection circuit, and running without a valid sensor signal could result in inefficient operation or stress on compressor components. It is best to address the fault before resuming normal use.

If the fix is simply reseating a dislocated connector, the cost is typically limited to a service call fee, which can range from around 75 to 150 dollars depending on your area. If the sensor needs replacement, parts and labor together may range from 100 to 300 dollars. A wiring harness repair or outdoor PCB replacement would fall at the higher end of that range or beyond, depending on parts availability and labor rates.

If the cause is a dislocated connector, a knowledgeable DIYer can reseat the connector at the outdoor PCB without specialized tools. However, if the wiring is broken or the sensor itself has failed, the repair involves working inside the outdoor unit and potentially handling refrigerant-adjacent components, which is better suited for a qualified technician. Always disconnect power to the unit before opening the outdoor cabinet.

A power reset may temporarily clear the error code, but if the underlying cause such as a loose connector, broken wire, or failed sensor is still present, the code will return once the unit attempts to read the sensor again. A reset alone is not a repair. The sensor circuit must be inspected and corrected to permanently resolve the fault.