Samsung Air Conditioner Error Code E251

The E251 error code on a Samsung air conditioner indicates a fault in the digital compressor discharge temperature sensor circuit. This sensor monitors the temperature of refrigerant gas leaving the compressor, a critical measurement used to protect the compressor from overheating and to regulate system operation. The error triggers when the sensor signal voltage falls outside the acceptable range, specifically above 4.95V or below 0.4V. The control board interprets these out-of-range voltages as either an open circuit (broken wire or failed sensor producing no signal) or a short circuit (wiring fault causing voltage to clamp at an extreme level). Importantly, the system only activates this detection logic when the outdoor ambient temperature is above -10 degrees Celsius, so the error will not appear during very cold operating conditions.

The discharge temperature sensor is a thermistor, meaning its electrical resistance changes in proportion to temperature. Under normal operation, the sensor produces a voltage signal within a defined window as the control board applies a reference voltage across the sensor and a fixed resistor. When the sensor resistance becomes infinite (open circuit) or near zero (short circuit), the resulting voltage reading falls outside the 0.4V to 4.95V window and triggers E251. Common failure points include the sensor itself, the wiring harness connecting the sensor to the outdoor control board, and the connector pins at either end of that circuit.

The first diagnostic step is to inspect the wiring and connector at the digital compressor discharge temperature sensor. Check for loose, corroded, or backed-out connector pins, and look for any visible damage to the sensor wiring harness such as chafing, pinching, or heat damage near the compressor body. If wiring and connectors check out, measure the sensor resistance directly to determine whether the sensor itself has failed.