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Error code reference

Samsung Air Conditioner Error Code 425

Outdoor compression ratio error / 3-phase reverse phase or phase fail detection

Samsung codesSamsung air conditioner codes

Outdoor compression ratio error / 3-phase reverse phase or phase fail detection - when 3-phase L1(R)-L2(S)-L3(T) order is reversed or a phase has no power.

First step from the service manual

Check 3-phase connection error; check if there is any problem with 3-phase detection part circuit; use 3-phase tester to verify phase order.

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

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What 425 means on a Samsung air conditioner

Samsung error code 425 indicates an outdoor compression ratio error tied specifically to 3-phase power supply issues. This code triggers when the outdoor unit detects that the three-phase electrical supply (L1/R, L2/S, L3/T) is either connected in the wrong rotational order (phase reversal) or that one of the three phases is entirely absent (phase loss or phase failure). The compressor in a 3-phase system relies on the correct phase sequence to rotate in the proper direction. If the phases are reversed, the compressor motor runs backward, which disrupts normal refrigerant compression and can cause serious mechanical damage. If a phase is missing entirely, the motor attempts to start on two phases and quickly enters a fault condition to prevent burnout.

The error originates from a dedicated 3-phase detection circuit within the outdoor unit's control board. This circuit continuously monitors phase sequence and voltage presence across all three input legs. When the detection circuit senses a reversal or dropout, it sends a fault signal to the main controller, which then locks out the compressor and generates code 425. Diagnosis requires a 3-phase tester to confirm the incoming phase rotation at the outdoor unit terminal block. Technicians should also inspect the detection circuit components on the control board for damage, failed capacitors, or poor solder connections, as a faulty detection board can generate a false 425 code even when utility power is correctly sequenced.

Source: manufacturer service documentation.

Common causes of 425

  1. 01

    Incorrect phase wiring order at the outdoor unit

    Wiring / connection

    During installation or after electrical service work, the L1, L2, and L3 conductors may be connected in the wrong sequence at the outdoor unit terminal block. Use a 3-phase rotation tester at the terminals to confirm correct L1(R)-L2(S)-L3(T) sequence.

  2. 02

    Phase loss from the supply side

    Wiring / connection

    A blown fuse, tripped breaker, or failed utility supply can knock out one phase entirely. Check voltage on all three legs at the disconnect and at the outdoor unit terminal block to confirm all three phases are live.

  3. 03

    Faulty 3-phase detection circuit on the outdoor control board

    Part replacement

    The detection circuit on the outdoor PCB can fail due to component damage or degraded solder joints, causing a false 425 error even when incoming power is correctly phased and fully present. If phase order and voltage are confirmed correct with a tester but the error persists, the control board is the likely culprit.

  4. 04

    Loose or corroded connections at the terminal block

    Wiring / connection

    A high-resistance connection or intermittent contact on one phase terminal can simulate a phase failure to the detection circuit. Inspect all terminal block connections for tightness, discoloration, or corrosion and torque to specification.

  5. 05

    Upstream wiring damage or failed disconnect components

    Part replacement

    Damaged conduit wiring between the distribution panel and the outdoor unit, or a failed fusible disconnect, can cause a phase dropout at the unit even when panel voltage is normal. Trace and test conductors from the panel to the outdoor unit terminal block.

See the test procedure for each cause

Frequently asked questions about 425

What does 425 mean on a Samsung air conditioner?
Error code 425 on a Samsung air conditioner signals a 3-phase power problem at the outdoor unit. Specifically, it means the unit has detected that the three power phases are connected in the wrong rotational order, or that one of the three phases has no voltage present. The system locks out the compressor automatically to prevent mechanical damage.
Can I fix error code 425 myself, or do I need a technician?
Some causes of error 425, such as swapped phase wiring at the terminal block, can be corrected by a qualified electrician without specialized HVAC tools. However, diagnosing the fault properly requires a 3-phase rotation tester, and any work on the high-voltage outdoor terminal block should only be performed by someone qualified to work on 3-phase electrical systems. If the outdoor control board's detection circuit has failed, board replacement is required.
Is it safe to keep running the air conditioner when error 425 is displayed?
No. Error 425 indicates the compressor is not receiving correct 3-phase power, and operating the system under these conditions risks serious compressor damage, motor winding failure, or electrical hazards. The unit will typically lock out the compressor automatically, but the underlying electrical fault should be resolved before attempting to restart the system.
Will resetting the unit clear error code 425?
A power reset will clear the active error code display, but the code will return immediately if the root cause has not been corrected. Because 425 is tied to a hard electrical fault, such as reversed phases or a missing phase, the error will reappear on the next startup attempt until the wiring issue or faulty detection circuit is properly repaired.
How much does it cost to repair a Samsung air conditioner showing error code 425?
Repair costs depend on the specific cause. If the fix is simply re-sequencing the phase wiring at the terminal block, labor costs from an electrician or HVAC technician may range from $75 to $200. If the outdoor control board's 3-phase detection circuit has failed and the board requires replacement, total parts and labor costs typically fall in the range of $300 to $700 or more depending on the unit model and regional labor rates.

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