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Error code reference

Samsung Air Conditioner Error Code P401

High temperature of discharge sensor

Samsung codesSamsung air conditioner codes

High temperature of discharge sensor – discharge temperature exceeding 135°C detected; system down on 2nd detection.

First step from the service manual

Check if both service valves are open.

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

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What P401 means on a Samsung air conditioner

The P401 error code on a Samsung air conditioner indicates that the discharge temperature sensor has detected a temperature exceeding 135°C at the compressor discharge line. The discharge line carries high-pressure, high-temperature refrigerant vapor from the compressor outlet to the condenser. When operating correctly, discharge temperatures remain within a safe range determined by refrigerant type, load conditions, and proper refrigerant charge. Exceeding 135°C signals that the compressor is working under abnormal stress, which can lead to compressor oil breakdown and permanent mechanical damage if not addressed.

The system is designed with a two-strike safety response: on the first detection of the overtemperature condition, a warning is registered, but on the second detection, the system shuts down completely to protect the compressor. This staged response helps distinguish between brief, transient spikes and a true sustained fault condition. The discharge temperature sensor itself is a thermistor mounted directly on or near the compressor discharge port, and its resistance values change with temperature; a failed or drifted sensor can trigger false P401 codes even when actual discharge temperatures are normal.

The most common root cause of genuinely high discharge temperatures is restricted refrigerant flow, which forces the compressor to work harder against abnormal pressure differentials. Closed or partially closed service valves are the first item to check, as they directly restrict refrigerant circulation. Low refrigerant charge, a blocked liquid line filter-drier, or a failing expansion valve can produce similar results. Inadequate airflow across the outdoor unit condenser coil, caused by dirt accumulation or a failing condenser fan motor, can also elevate discharge temperatures by reducing the system's ability to reject heat.

Source: manufacturer service documentation.

Common causes of P401

  1. 01

    Closed or partially closed service valves

    Wiring / connection

    If the liquid or suction service valves on the outdoor unit are not fully open, refrigerant flow is restricted and compressor discharge temperatures rise rapidly. Visually inspect both service valves and confirm they are fully backseated (open).

  2. 02

    Low refrigerant charge

    Wiring / connection

    An undercharged system causes the compressor to operate with insufficient refrigerant mass flow, resulting in elevated compression ratios and high discharge temperatures. A technician should check system pressures and inspect for leaks before recharging.

  3. 03

    Restricted or dirty condenser coil or failed condenser fan

    Part replacement

    A fouled condenser coil or a condenser fan motor that is running slowly or not at all reduces heat rejection, driving up head pressure and discharge temperature. Inspect the coil for debris and confirm the fan runs at correct speed when the unit operates.

  4. 04

    Blocked liquid line filter-drier or restricted expansion valve

    Part replacement

    A saturated or restricted filter-drier or a malfunctioning expansion valve starves the evaporator of refrigerant and causes the compressor to run in a low-suction, high-discharge pressure condition. Technicians can identify this by checking the pressure differential across the filter-drier or measuring subcooling values.

  5. 05

    Faulty discharge temperature sensor

    Part replacement

    A thermistor that has drifted out of calibration or developed an open circuit can report false overtemperature readings even when actual discharge temperatures are within normal range. Compare the sensor resistance value against the temperature-resistance table for the specific sensor to confirm accuracy.

See the test procedure for each cause

Frequently asked questions about P401

What does P401 mean on a Samsung air conditioner?
P401 indicates that the discharge temperature sensor detected a temperature above 135°C at the compressor outlet. Samsung's control logic triggers a full system shutdown on the second detection of this condition to prevent compressor damage. The fault points to either a genuine overtemperature condition in the refrigerant circuit or a faulty discharge sensor.
Can I fix P401 myself, or do I need a technician?
The one check a non-technician can perform is confirming that both service valves on the outdoor unit are fully open. Beyond that, diagnosing low refrigerant charge, checking pressures, inspecting the expansion valve, or replacing the discharge sensor requires refrigeration tools and certifications. It is strongly recommended to call a qualified HVAC technician for further diagnosis.
Is it safe to keep running my air conditioner with a P401 error?
No. The system will shut itself down on the second overtemperature detection specifically to protect the compressor from heat-related damage. Attempting to reset the unit and continue running it without resolving the root cause risks permanent compressor failure, which is one of the most expensive repairs on any air conditioning system.
Will resetting the unit clear the P401 error code?
A power reset may temporarily clear the fault and allow the system to restart, but if the underlying cause is still present, the P401 code will return and the system will shut down again on the second detection. Clearing the code without addressing the root cause does not fix the problem and increases the risk of compressor damage.
How much does it cost to repair a P401 error on a Samsung air conditioner?
Repair costs vary widely depending on the cause. If the fix is simply opening a closed service valve or cleaning a dirty condenser coil, costs may be limited to a service call fee, typically in the range of $75 to $200. If the system needs refrigerant, a replacement filter-drier, or a new discharge sensor, costs can range from $150 to $600 or more. A compressor replacement, in a worst-case scenario where the component has already been damaged, can cost $800 to $2,500 or higher depending on system size.

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