Samsung Air Conditioner Error Code 123

Error code 123 on a Samsung air conditioner indicates a fault with the indoor unit heat exchanger outlet temperature sensor, also referred to as the OUT sensor or out-temp sensor. This sensor monitors the refrigerant temperature as it exits the indoor heat exchanger coil, providing critical feedback to the control board for regulating cooling and heating cycles. When the control board detects a signal from this sensor that falls outside the expected resistance range, either reading as an open circuit or a short circuit, it triggers error code 123 and halts normal operation to prevent equipment damage.

The three primary hardware conditions that cause this fault are connector dislocation, wire breakage, and a defective sensor itself. A displaced connector at either the sensor end or the control board end will interrupt the signal circuit, causing the board to read an open circuit. A broken wire in the sensor harness produces the same open-circuit condition. A short circuit, where the sensor wiring contacts ground or another conductor, typically results from damaged wire insulation. In either case, the control board cannot obtain a valid temperature reading and logs the error.

Diagnosis begins at the wiring harness. The sensor wire running from the out-temp sensor to the indoor unit control board should be inspected along its full length for visible damage, pinching, or corrosion at the connector pins. After confirming wiring integrity, the sensor itself can be tested by measuring its resistance across its terminals and comparing the reading to the expected resistance curve for the operating temperature. A sensor that reads open, shorted, or significantly out of range at a known temperature must be replaced.