Samsung Air Conditioner Error Code E257

Error code E257 on a Samsung air conditioner indicates a fault with the discharge temperature sensor on fixed scroll compressor 2. This sensor monitors the temperature of refrigerant gas as it exits the compressor head, which is a critical measurement for protecting the compressor from overheating. The error is triggered when the sensor circuit voltage falls outside the acceptable operating window: a reading above 4.95V corresponds to an open circuit condition and maps to an apparent temperature below -30C, while a reading below 0.5V indicates a short circuit condition and maps to an apparent temperature above 151C. Either condition causes the control board to reject the sensor data as invalid and flag the fault.

The fixed scroll compressor 2 is the second compressor in a multi-compressor system, typically found in larger capacity or multi-zone Samsung units. The discharge temperature sensor is a thermistor-type device whose resistance changes predictably with temperature, and the control board interprets the resulting voltage divider output to calculate actual temperature. When the circuit is open, resistance is effectively infinite and voltage spikes toward the supply rail. When shorted, resistance drops to near zero and voltage collapses. Both failure modes prevent accurate temperature monitoring and require the system to shut down the affected compressor to avoid damage.

The first step in diagnosing E257 is physically inspecting the wiring harness and connector for the compressor 2 discharge sensor. Broken wires, corroded terminals, loose connector pins, or damaged insulation from heat exposure near the compressor head are the most common root causes. If the wiring checks out, the thermistor itself should be tested for correct resistance at a known temperature and replaced if readings fall outside the expected curve.