Samsung Air Conditioner Error Code E321

The Samsung air conditioner error code E321 indicates a fault with the EVI IN temperature sensor located in the outdoor unit. EVI stands for Enhanced Vapor Injection, a refrigerant circuit feature used in heat pump systems to improve efficiency and heating capacity at low ambient temperatures. The EVI IN sensor monitors the temperature of refrigerant entering the vapor injection circuit, and the outdoor PCB continuously reads this signal to regulate system operation. When the signal falls outside the expected range, the unit logs E321 and may suspend operation to prevent component damage.

The three primary causes identified for this fault are connector dislocation, wire breakage, and a defective sensor. A dislocated connector is the most common trigger and occurs when the sensor plug separates from its socket on the outdoor PCB, either from vibration over time or during a previous service visit. Wire breakage can occur anywhere along the sensor harness, particularly at stress points near cable clamps or routing bends. A defective sensor itself means the thermistor element has failed and is producing an out-of-range resistance value that the PCB cannot interpret as a valid temperature reading.

Diagnosis should begin at the outdoor unit by inspecting the EVI IN sensor connector on the PCB. If the connector is seated properly, the next step is to check the sensor's resistance using a multimeter and compare the reading against the expected resistance-temperature curve for that sensor type. The wiring harness should also be inspected along its full length for visible damage, chafing, or breaks. If resistance is outside the acceptable range despite intact wiring and a secure connection, sensor replacement is required.