Samsung Air Conditioner Error Code 321

Error code 321 on a Samsung air conditioner indicates a fault in the EVI inlet temperature sensor circuit. The control board has detected either an open or short circuit in the sensor, which can be caused by a disconnected connector, a broken wire, or a failed thermistor. The EVI system is used in heat pump models to enhance heating performance at low outdoor temperatures, so this fault can significantly impact heating capacity.

Error 321 is a sensor circuit fault rather than a direct safety hazard to the home. However, operating the unit without a functioning EVI temperature sensor can prevent proper system control and may lead to refrigerant circuit issues over time. It is advisable to have the fault diagnosed and repaired promptly rather than continuing to run the system with the error active.

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 control board re-evaluates the circuit. Resetting is useful for confirming whether a fault was intermittent, such as a connector that reseated on its own, but it does not repair a broken wire or failed sensor. A proper diagnostic check of the sensor and wiring is necessary to resolve the fault permanently.

Some causes of error 321 can be addressed without specialized tools, such as reseating a loose sensor connector or inspecting visible wiring for obvious damage. However, confirming a sensor failure requires measuring thermistor resistance with a multimeter and comparing it to a temperature-resistance specification. Replacing the sensor or tracing internal wire breaks involves working inside the unit and is best handled by a qualified technician.

Repair costs depend on the root cause. If the fix is simply reseating a connector, there may be little to no parts cost and only a service call fee, typically in the range of $75 to $150. If the EVI temperature sensor itself needs replacement, parts and labor combined can range from $150 to $350 or more depending on the model and local labor rates.