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Samsung Air Conditioner Error Code E399

Heat sink temperature sensor error of Fan2.

Samsung codesSamsung air conditioner codes

Heat sink temperature sensor error of Fan2.

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What E399 means on a Samsung air conditioner

Error code E399 on a Samsung air conditioner indicates a heat sink temperature sensor fault associated with the Fan2 module. The heat sink temperature sensor is a thermistor mounted directly on or near the heat sink of the inverter drive board or power module for the second fan circuit. Its primary function is to monitor the thermal state of the power electronics during operation, allowing the control system to prevent overheating damage to the switching transistors and related components. When the sensor signal falls outside the expected resistance or voltage range, the system flags E399 and may shut down Fan2 operation to protect the hardware.

The fault can originate from the sensor itself, the wiring harness connecting it to the control board, or the control board's input circuitry. A failed thermistor will typically present as an open circuit or a short, both of which produce readings outside the normal operating window. Corroded or damaged connector pins in the sensor harness can cause intermittent or incorrect resistance readings that trigger the error under load or at specific temperatures.

In some cases, the heat sink itself may be running at extreme temperatures due to blocked airflow, a failing fan motor, or inadequate refrigerant charge, which could push sensor readings beyond their acceptable range even with a functioning sensor. Technicians should assess both the electrical integrity of the sensor circuit and the physical cooling conditions around the Fan2 power module before condemning any single component.

Source: manufacturer service documentation.

Common causes of E399

  1. 01

    Faulty heat sink thermistor

    Part replacement

    The thermistor sensor itself may have failed, presenting an open circuit or short circuit that sends an out-of-range signal to the control board. Measuring the sensor's resistance and comparing it to the expected value for a given temperature will confirm this fault.

  2. 02

    Damaged or corroded sensor wiring harness

    Wiring / connection

    The wiring or connector pins between the thermistor and the control board may be corroded, broken, or intermittently disconnected. Visually inspecting the harness and checking for continuity with a multimeter can identify this issue.

  3. 03

    Control board input circuit failure

    Part replacement

    The sensor input circuit on the main or inverter control board may have failed, causing it to misread an otherwise functional sensor. If the sensor and wiring check out correctly, the board itself may need replacement.

  4. 04

    Overheating due to restricted airflow

    Wiring / connection

    Blocked vents, dirty filters, or a failing Fan2 motor can cause the heat sink to operate at excessively high temperatures, pushing sensor readings out of range. Check for obstructions and verify the fan motor is spinning freely and at the correct speed.

  5. 05

    Poor sensor mounting contact

    Wiring / connection

    If the thermistor has come loose from the heat sink surface, it will no longer accurately reflect actual heat sink temperatures and may produce erratic readings. Inspect the physical mounting of the sensor and reattach or resecure it as needed.

See the test procedure for each cause

Frequently asked questions about E399

What does E399 mean on a Samsung air conditioner?
E399 indicates a heat sink temperature sensor error for the Fan2 module on your Samsung air conditioner. The sensor monitors the temperature of the power electronics associated with the second fan circuit, and the control system has detected a reading outside the acceptable range. This can result from a failed sensor, wiring issues, or an actual overheating condition at the heat sink.
Can I fix E399 myself, or do I need a technician?
Some basic checks, such as inspecting for blocked airflow and cleaning filters, can be done without professional help. However, diagnosing the thermistor, testing the wiring harness for continuity, and evaluating the control board requires electrical testing tools and knowledge of inverter drive circuits. Most homeowners will need a qualified HVAC technician to resolve this error safely and correctly.
Is it safe to run my air conditioner with the E399 error active?
It is not recommended to continue running the unit while E399 is active. The error indicates a fault in the thermal protection circuit for the Fan2 module, which means the system may not be able to detect or respond to overheating conditions in the power electronics. Continued operation without resolving the fault could result in damage to the inverter board or related components.
Will resetting my Samsung air conditioner clear the E399 error?
A power reset may temporarily clear the error code, but if the underlying fault persists, the code will return once the unit resumes operation and the control system re-evaluates the sensor signal. Resetting is useful for ruling out a transient fault, but a recurring E399 requires proper diagnosis of the sensor, wiring, and control board.
How much does it cost to repair an E399 error on a Samsung air conditioner?
Repair costs depend on the root cause. Replacing a thermistor sensor is generally on the lower end of the cost spectrum, typically in the range of $75 to $200 including labor. If the control board or inverter module requires replacement, costs can range from $300 to $700 or more depending on the model and local labor rates. A diagnostic service call is usually required first to confirm the faulty component.

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