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Error code reference

Samsung Air Conditioner Error Code E420

SUMP TEMP DIGITAL sensor OPEN/SHORT error. Detected when outdoor temp over -10°C. Error level

Samsung codesSamsung air conditioner codes

SUMP TEMP DIGITAL sensor OPEN/SHORT error. Detected when outdoor temp over -10°C. Error level: Over 4.95V (-30°C), below 0.5V (151°C).

First step from the service manual

Check sensor connector; measure resistance across both terminals.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E420 means on a Samsung air conditioner

The E420 error code on a Samsung air conditioner indicates an open or short circuit fault in the sump temperature digital sensor. This sensor monitors the temperature of the sump, which is the lower portion of the outdoor unit where refrigerant oil or condensate collects. The control board evaluates the sensor's output voltage to determine whether a fault condition exists. Specifically, the error triggers when the outdoor ambient temperature is above -10 degrees Celsius and the sensor voltage reads above 4.95V, corresponding to an out-of-range low temperature reading below -30 degrees Celsius, or below 0.5V, corresponding to an out-of-range high temperature reading above 151 degrees Celsius. These voltage thresholds indicate either a broken circuit (open) or a direct short in the sensor circuit.

The sump temperature sensor is a negative temperature coefficient (NTC) thermistor. As temperature increases, its resistance decreases, which causes the voltage signal sent to the control board to drop accordingly. When the resistance goes to near-zero (a short), the voltage collapses below 0.5V. When the circuit breaks entirely (an open), the voltage rises above 4.95V. Either condition causes the unit to halt operation and display E420 to prevent compressor damage or unsafe operating conditions.

Diagnosis begins with inspecting the sensor connector at the outdoor unit control board for corrosion, bent pins, or loose seating. After confirming the connector is secure, measuring resistance across both sensor terminals will reveal whether the thermistor itself has failed. A reading of zero ohms confirms a short; an infinite or open reading confirms a broken sensor. Wiring between the sensor and the board should also be inspected for pinching, abrasion, or moisture intrusion.

Source: manufacturer service documentation.

Common causes of E420

  1. 01

    Failed NTC thermistor sensor

    Part replacement

    The sump temperature sensor itself has developed an internal open or short circuit. This is the most frequent cause and is confirmed by measuring resistance across the sensor terminals, where a reading of zero ohms or infinite resistance indicates a defective sensor.

  2. 02

    Loose or disconnected sensor connector

    Wiring / connection

    The connector linking the sensor to the control board may have vibrated loose or been dislodged during service. Inspecting the connector at the board and reseating it firmly is the first physical check to perform.

  3. 03

    Corroded or damaged connector pins

    Wiring / connection

    Moisture intrusion into the outdoor unit can cause oxidation on the sensor connector pins, increasing resistance in the circuit and producing out-of-range voltage signals. Visual inspection will reveal discoloration or pitting on the terminals.

  4. 04

    Damaged sensor wiring

    Part replacement

    The wire harness running from the sump sensor to the control board may be pinched, abraded, or cracked due to vibration or physical contact with moving components. A continuity check along the full wire length will identify any break or short.

  5. 05

    Faulty outdoor unit control board

    Part replacement

    If the sensor and wiring both test within normal parameters, the control board's sensor input circuit may have failed, causing it to misread the sensor voltage. This is the least common cause and should only be concluded after all other components check out.

See the test procedure for each cause

Frequently asked questions about E420

What does E420 mean on a Samsung air conditioner?
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.
Can I fix the E420 error myself?
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.
Is it safe to run my air conditioner with the E420 error showing?
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.
Will resetting the air conditioner clear the E420 error?
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.
How much does it cost to repair an E420 error on a Samsung air conditioner?
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.

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