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Error code reference

Samsung Air Conditioner Error Code P408

Low pressure sensor protection

Samsung codesSamsung air conditioner codes

Low pressure sensor protection – low pressure less than 3 kg/cm²G (cooling) or 0.5 kg/cm²G (heating).

First step from the service manual

Check indoor unit fan motor; check EEV; check refrigerant charge.

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

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What P408 means on a Samsung air conditioner

The P408 error code on Samsung air conditioners indicates a low pressure sensor protection fault. The system monitors suction-side refrigerant pressure continuously through a low pressure sensor. During cooling operation, if pressure drops below 3 kg/cm²G, or during heating operation, if pressure falls below 0.5 kg/cm²G, the unit triggers P408 and shuts down to prevent compressor damage. Low suction pressure is a sign the refrigerant circuit is not delivering adequate vapor pressure back to the compressor, which reduces lubrication and cooling capacity and can lead to compressor failure if ignored.

The three primary areas to inspect are the indoor unit fan motor, the electronic expansion valve (EEV), and the refrigerant charge. A failed or underperforming indoor fan motor reduces airflow across the evaporator coil, causing refrigerant to remain in a liquid state too long and pulling suction pressure down abnormally. A malfunctioning EEV that is stuck closed or throttled too far will restrict refrigerant flow, starving the suction side. Low refrigerant charge, whether from an original undercharge or a leak in the system, directly reduces suction pressure and is a very common cause of this fault.

Diagnosing P408 requires gauges on the suction port to confirm actual operating pressure against the specified thresholds. Technicians should verify indoor fan operation at full speed, inspect EEV wiring and coil resistance, and check for oil staining or frost patterns that suggest a refrigerant leak. Refrigerant recovery, leak repair, and proper recharge to factory specifications are required before the system can operate safely.

Source: manufacturer service documentation.

Common causes of P408

  1. 01

    Low or lost refrigerant charge

    Part replacement

    A refrigerant leak or an original undercharge reduces suction pressure directly. Look for oil staining around fittings, frost buildup on the suction line, or pressure readings clearly below the 3 kg/cm²G cooling threshold.

  2. 02

    Malfunctioning electronic expansion valve (EEV)

    Part replacement

    An EEV that is stuck in a closed or over-restricted position starves the evaporator of refrigerant, dropping suction pressure. Check EEV coil resistance and wiring connections, and listen for the valve stepping during startup.

  3. 03

    Indoor unit fan motor failure or reduced airflow

    Part replacement

    A weak or failed indoor fan motor reduces evaporator airflow, causing refrigerant to absorb heat too slowly and pulling suction pressure below safe limits. Confirm the fan runs at full commanded speed and check for blocked filters or coils.

  4. 04

    Blocked or dirty indoor coil or air filter

    Wiring / connection

    Heavy dirt buildup on the indoor evaporator coil or air filter restricts airflow similar to a fan failure, reducing heat exchange and lowering suction pressure. Inspect and clean both before replacing components.

  5. 05

    Faulty low pressure sensor

    Part replacement

    If refrigerant pressures are confirmed to be within normal range on gauges but P408 still triggers, the low pressure sensor itself may be reading incorrectly. Compare sensor output voltage to known-good values and replace the sensor if it is out of range.

See the test procedure for each cause

Frequently asked questions about P408

What does P408 mean on a Samsung air conditioner?
P408 is a low pressure sensor protection fault. It activates when suction-side refrigerant pressure falls below 3 kg/cm²G during cooling or below 0.5 kg/cm²G during heating. The unit shuts down to protect the compressor from running under abnormally low refrigerant pressure conditions.
Can I fix P408 myself without a technician?
Some steps, like cleaning a dirty air filter or checking that the indoor fan is spinning freely, can be done without special tools. However, diagnosing and correcting refrigerant charge or repairing an EEV requires EPA certification and refrigerant handling equipment. If the fault is related to refrigerant levels or valve components, a licensed HVAC technician is required.
Is it safe to keep running the unit when P408 appears?
No. The unit should not be forced to run while P408 is active. Operating a compressor under low suction pressure reduces lubrication, causes overheating of compressor internals, and can result in permanent compressor failure. Leave the unit off until the root cause has been diagnosed and corrected.
How much does it cost to repair a P408 fault on a Samsung air conditioner?
Repair costs vary widely depending on the cause. A refrigerant leak repair and recharge typically runs anywhere from $200 to $600 or more depending on refrigerant type and leak location. An EEV replacement can range from $150 to $400 in parts and labor. A failed indoor fan motor repair generally falls between $100 and $350.
Will resetting the unit clear the P408 error code?
A power reset may temporarily clear the code and allow the unit to restart, but if the underlying cause has not been fixed, the low pressure condition will return and P408 will reactivate. Repeatedly resetting the unit without repairing the fault risks compressor damage. A reset is only appropriate as part of a diagnostic process after the fault has been identified and corrected.

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