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Error code reference

Samsung Air Conditioner Error Code E255

MCU temperature sensor open/short error.

Samsung codesSamsung air conditioner codes

MCU temperature sensor open/short error.

First step from the service manual

Check if MCU temperature sensor connector is disconnected from PCB; measure resistance across terminals.

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

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  • Wiring diagram references and connector pinouts from the OEM service manual
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What E255 means on a Samsung air conditioner

The E255 error code on a Samsung air conditioner indicates a fault with the MCU (microcontroller unit) temperature sensor, specifically an open circuit or short circuit condition. The MCU temperature sensor monitors the temperature of the main control board's microcontroller chip, allowing the system to detect overheating conditions and adjust operation accordingly. When the PCB cannot read a valid signal from this sensor, it triggers the E255 fault and may limit or shut down system operation to prevent damage.

An open circuit fault means the electrical path through the sensor has been broken, resulting in no signal reaching the PCB. This can occur due to a disconnected connector, a broken wire in the harness, or a failed sensor with internal wire breakage. A short circuit fault means unintended continuity exists between sensor terminals or between a terminal and ground, producing an out-of-range resistance reading that the PCB interprets as invalid. Both conditions prevent accurate temperature monitoring of the MCU.

The first diagnostic step is to inspect the MCU temperature sensor connector at the PCB for any signs of disconnection, corrosion, or bent pins. After confirming the connector is fully seated, measure resistance across the sensor terminals. A functional NTC-type temperature sensor will show a specific resistance value relative to ambient temperature. An open circuit will read infinite resistance (OL on a multimeter), while a short circuit will read near zero ohms. Either extreme confirms sensor or wiring failure requiring component replacement.

Source: manufacturer service documentation.

Common causes of E255

  1. 01

    Disconnected sensor connector at PCB

    Wiring / connection

    The MCU temperature sensor connector may have come loose from the main PCB due to vibration or handling during prior service. Inspect the connector carefully and reseat it firmly to restore contact.

  2. 02

    Failed MCU temperature sensor (open circuit)

    Part replacement

    The sensor itself may have developed an internal break, resulting in infinite resistance across its terminals. This will be confirmed when a multimeter reads OL across the sensor terminals with the connector removed.

  3. 03

    Shorted MCU temperature sensor

    Part replacement

    Internal failure of the sensor can cause a short circuit, producing near-zero resistance across terminals. A multimeter reading close to 0 ohms across the sensor terminals indicates this condition.

  4. 04

    Damaged wiring harness

    Part replacement

    The wire leads between the sensor and the PCB connector may be pinched, chafed, or broken, causing an open or short condition in the circuit rather than at the sensor itself. Inspect the full length of the harness for visible damage.

  5. 05

    Corroded or damaged connector terminals

    Wiring / connection

    Moisture or oxidation on the sensor connector pins can create high resistance or intermittent contact, mimicking an open circuit fault. Clean terminals with electrical contact cleaner and check for bent or pushed-back pins.

See the test procedure for each cause

Frequently asked questions about E255

What does E255 mean on a Samsung air conditioner?
E255 indicates an open circuit or short circuit fault with the MCU temperature sensor on the main PCB. This sensor monitors the temperature of the microcontroller unit on the control board. When the PCB cannot read a valid resistance signal from the sensor, it triggers this error and may suspend normal operation to protect the electronics.
Can I fix the E255 error myself?
Some causes of E255 are DIY-friendly, such as reseating a loose connector or cleaning corroded terminals. You will need a multimeter to measure resistance across the sensor terminals to determine whether the sensor itself has failed. If the sensor or wiring harness needs replacement, comfort with basic electrical work and component sourcing is required. If you are unsure about working around control board components, a qualified technician is recommended.
Is it safe to run my Samsung air conditioner with the E255 error showing?
It is not advisable to continue operating the unit while the E255 error is active. The MCU temperature sensor exists to protect the control board from overheating, and without a valid reading, the system has no way to detect a developing overheat condition. Continued operation could risk damage to the PCB or other electrical components.
How much does it cost to repair the E255 error on a Samsung air conditioner?
If only the sensor connector needs reseating or cleaning, there may be no parts cost, though a service call will carry a labor fee typically in the range of $75 to $150. If the MCU temperature sensor itself requires replacement, parts and labor combined generally range from $100 to $300 depending on the specific unit model and local labor rates. Control board replacement, if the board is also damaged, can increase costs significantly.
Will resetting my Samsung air conditioner clear the E255 error?
A power reset may temporarily clear the E255 error code, but if the underlying sensor fault still exists, the error will return once the unit attempts to read the sensor again. A reset alone does not repair a disconnected connector, damaged wiring, or a failed sensor. Proper diagnosis and correction of the root cause are required for a lasting resolution.

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