Samsung Air Conditioner Error Code E420

E420 indicates an open or short circuit fault in the sump temperature sensor located in the outdoor unit. The control board detected a sensor voltage above 4.95V or below 0.5V while the outdoor temperature was above -10 degrees Celsius, which represents an impossible reading. The unit shuts down to prevent compressor damage until the fault is resolved.

No, you should not attempt to override or continue operating the unit while E420 is active. The system has intentionally shut down because the control board cannot verify sump temperature, which is needed to protect the compressor from damage. Running the unit without reliable sensor data could cause compressor overheating or other mechanical failures.

Repair costs vary depending on which component has failed. Replacing the sump temperature sensor typically ranges from around 50 to 150 dollars in parts, plus labor costs that can range from 75 to 200 dollars depending on your location and the technician's rates. If the control board itself has failed, parts costs can range from 150 to 400 dollars or more, making board replacement significantly more expensive.

Some basic checks are within reach for a knowledgeable DIYer, including visually inspecting the sensor connector at the outdoor unit and reseating it if it appears loose. However, accurately measuring thermistor resistance requires a multimeter and knowledge of how to access the outdoor control board safely. If the sensor or wiring needs replacement, working inside the outdoor unit involves electrical components that should be handled with caution and ideally by a qualified technician.

A power reset may temporarily clear the error display, but the code will return as soon as the control board re-evaluates the sensor signal. Because the fault is triggered by a hardware condition, such as a failed thermistor or damaged wire, resetting the unit does not address the underlying problem. The sensor circuit must be inspected and repaired before the error will clear permanently.