Samsung Air Conditioner Error Code E311

The E311 error code on a Samsung air conditioner indicates a fault with the sump temperature digital sensor, also referred to as the sump thermistor. This sensor monitors the temperature of the compressor oil sump in the outdoor unit, which is critical for protecting the compressor from operating under unsafe thermal conditions. The error is triggered when the outdoor ambient temperature is above -10°C and the sensor signal voltage either rises above 4.95V (corresponding to an open circuit condition reading approximately -30°C) or drops below 0.5V (corresponding to a short circuit condition reading approximately 151°C). These voltage thresholds define the boundaries of a valid sensor signal, and readings outside them indicate the sensor or its circuit has failed.

The two failure modes are an open circuit and a short circuit. An open circuit, indicated by voltage above 4.95V, typically results from a broken wire, a disconnected connector, or a failed thermistor element that has lost continuity. A short circuit, indicated by voltage below 0.5V, occurs when the sensor wiring contacts ground or another conductor improperly, or when the thermistor itself has internally shorted. Because this sensor is located in the outdoor unit and exposed to vibration, moisture, and temperature cycling, connector corrosion and wire chafing are common physical causes.

Diagnosis begins by inspecting whether the sensor connector has separated from the outdoor unit PCB, which is a frequent cause of the open circuit condition. If the connector is secure, the technician should measure the sensor resistance directly across the thermistor terminals and compare it against the expected resistance curve for the operating temperature. Wiring between the sensor and the control board should also be checked for damage, pinching, or corrosion at the connector pins.