Samsung Air Conditioner Error Code E123

The Samsung E123 error code indicates a fault with the indoor heat exchanger evaporator outlet (EVAP OUT) temperature sensor. This sensor monitors the refrigerant temperature at the outlet point of the indoor evaporator coil and feeds that data to the control board to regulate cooling cycles, prevent freeze-up, and optimize system efficiency. When the control board detects a signal outside the expected resistance range, either an open circuit (infinite resistance) or a short circuit (near-zero resistance), it triggers the E123 fault and halts normal operation to protect the system.

The three root causes identified for this fault are connector dislocation, wire breakage, or a defective sensor itself. Connector dislocation occurs when the sensor plug separates from its mating connector on the control board or along the wiring harness, breaking the signal path. Wire breakage typically results from physical damage, pinching during installation, or long-term vibration fatigue causing the conductor inside the insulation to fracture. A defective sensor means the thermistor element inside the sensor body has failed electrically, producing a resistance value outside the acceptable operating range regardless of actual temperature.

Diagnosis begins with a physical inspection of the EVAP OUT sensor wiring. The technician should trace the sensor wire from the sensor body mounted on the evaporator coil outlet through the harness to the indoor unit control board, checking for any visible breaks, kinks, or disconnected plugs. If the wiring appears intact, resistance testing across the sensor terminals with a multimeter will confirm whether the thermistor itself is within specification or has failed open or shorted internally.