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Error code reference

Samsung Air Conditioner Error Code 31

Outdoor unit discharge temperature sensor error (open or short).

Samsung codesSamsung air conditioner codes

Outdoor unit discharge temperature sensor error (open or short).

First step from the service manual

Check discharge temperature sensor resistance at PIN#3,4 of CN51 on outdoor control board.

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

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What 31 means on a Samsung air conditioner

Samsung air conditioner error code 31 indicates a fault with the outdoor unit discharge temperature sensor. This sensor monitors the refrigerant temperature at the compressor discharge line, which is a critical measurement used by the control system to protect the compressor from overheating and to regulate system operation. The error is triggered when the outdoor control board detects either an open circuit or a short circuit condition in the sensor circuit, meaning the signal falls outside the expected resistance range for any valid temperature reading.

The discharge temperature sensor is a negative temperature coefficient (NTC) thermistor, meaning its resistance decreases as temperature increases. The outdoor control board reads this resistance through PIN#3 and PIN#4 of connector CN51. An open circuit condition produces an abnormally high or infinite resistance reading, while a short circuit produces a near-zero resistance reading. Both conditions tell the board that the sensor input is unreliable, prompting the error code and typically shutting down or limiting compressor operation to prevent damage.

Common root causes include a failed thermistor, damaged wiring between the sensor and the control board, corroded or loose connector pins at CN51, or physical damage to the sensor from vibration or refrigerant line contact. Starting diagnosis at PIN#3 and PIN#4 of CN51 with a multimeter allows a technician to confirm whether the fault is in the sensor itself, the wiring harness, or the connector interface before replacing any components.

Source: manufacturer service documentation.

Common causes of 31

  1. 01

    Failed discharge temperature sensor

    Part replacement

    The NTC thermistor itself has failed internally, producing an open or short circuit reading. Confirm by measuring resistance across PIN#3 and PIN#4 of CN51 on the outdoor control board and comparing the reading against the expected resistance curve for the ambient temperature.

  2. 02

    Damaged or broken sensor wiring

    Part replacement

    The wiring harness running from the discharge sensor to the outdoor control board may be cut, pinched, or broken, causing an open circuit. Visually inspect the wires along their entire route for abrasion, pinch points near sheet metal edges, or contact with hot refrigerant lines.

  3. 03

    Corroded or loose connector at CN51

    Wiring / connection

    Corrosion, moisture intrusion, or a partially seated connector at PIN#3 and PIN#4 of CN51 can interrupt the sensor signal. Disconnect the connector, inspect the pins for oxidation or bent contacts, and reseat it firmly before replacing any parts.

  4. 04

    Sensor dislodged from mounting position

    Wiring / connection

    The discharge temperature sensor may have vibrated loose from its clip or mounting bracket on the refrigerant line, causing erratic or invalid readings. Check that the sensor tip is properly secured and in firm contact with the discharge line.

  5. 05

    Faulty outdoor control board

    Part replacement

    If the sensor and all wiring check out correctly but the error persists, the input circuit on the outdoor control board at CN51 may have failed. This is the least likely cause and should only be considered after the sensor, wiring, and connector have been ruled out.

See the test procedure for each cause

Frequently asked questions about 31

What does 31 mean on a Samsung air conditioner?
Error code 31 on a Samsung air conditioner indicates a discharge temperature sensor fault on the outdoor unit. The outdoor control board has detected either an open circuit or a short circuit in the sensor connected at PIN#3 and PIN#4 of connector CN51. This sensor monitors refrigerant temperature leaving the compressor, and without a valid reading, the system limits or stops operation to protect the compressor.
Can I fix error code 31 on my Samsung air conditioner myself?
Some basic checks are accessible to a knowledgeable DIYer, such as inspecting the wiring harness for visible damage and reseating the connector at CN51 on the outdoor control board. However, accurately diagnosing an open or short circuit in the sensor requires a multimeter and familiarity with reading thermistor resistance values. Replacing the sensor or the outdoor control board is best handled by a qualified technician, especially since working inside the outdoor unit involves electrical components.
Is it safe to run my Samsung air conditioner with error code 31 active?
It is not recommended to continue operating the unit with error code 31 active. The discharge temperature sensor is a key compressor protection input, and without a valid reading the control system cannot properly guard against overheating. Running the system in this condition risks compressor damage, which is significantly more expensive to repair than the sensor itself.
How much does it cost to repair Samsung air conditioner error code 31?
Repair costs vary depending on the root cause. A replacement discharge temperature sensor typically falls in the range of $15 to $60 for the part alone, while labor charges for an HVAC technician can add $75 to $200 depending on your region and the complexity of access. If the fault turns out to be a failed outdoor control board, part costs can range from $150 to $400 or more, making a proper diagnosis before ordering parts especially important.
Will resetting my Samsung air conditioner clear error code 31?
A power reset may temporarily clear the error code display, but the fault will return as soon as the outdoor control board re-reads the sensor signal at CN51 and detects the open or short circuit again. Because the underlying cause is a hardware fault in the sensor or wiring rather than a software glitch, clearing the code without repairing the sensor circuit will not restore normal operation.

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