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Error code reference

Samsung Air Conditioner Error Code P428

Outdoor unit compression rate 1 error

Samsung codesSamsung air conditioner codes

Outdoor unit compression rate 1 error - compression ratio over 8.5 for 5 minutes.

First step from the service manual

Check service valves; check PWM valve coil and connector.

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

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What P428 means on a Samsung air conditioner

Error code P428 on a Samsung air conditioner indicates an outdoor unit compression ratio error. Specifically, the system has detected that the compression ratio across compressor 1 has exceeded 8.5 and remained above that threshold continuously for 5 minutes. The compression ratio is calculated by comparing discharge pressure to suction pressure. When this ratio climbs too high, it signals that the compressor is working far beyond normal operating parameters, which can indicate a refrigerant flow restriction, a pressure imbalance, or a failure in a component responsible for regulating refrigerant movement.

The most immediate items to investigate are the service valves on the outdoor unit. If either the liquid or vapor service valve is partially or fully closed, refrigerant flow is restricted, suction pressure drops, and discharge pressure rises, rapidly pushing the compression ratio above the 8.5 limit. Beyond the service valves, the PWM (pulse-width modulation) expansion valve is a key suspect. The PWM valve controls refrigerant metering into the evaporator, and if its coil has failed or its connector has become loose or corroded, the valve may not open properly, starving the low side of refrigerant and creating the same pressure imbalance.

If service valves are confirmed open and the PWM valve coil and connector check out, further diagnosis should include verifying that refrigerant charge is within specification, checking for non-condensables in the system, and inspecting the outdoor coil for blockage or restricted airflow. A persistently high compression ratio under normal ambient conditions often points to low refrigerant charge or a partially blocked expansion device as the root cause.

Source: manufacturer service documentation.

Common causes of P428

  1. 01

    Closed or partially closed service valve

    Wiring / connection

    If the liquid or suction service valve on the outdoor unit is not fully open, refrigerant flow is restricted, causing suction pressure to drop and discharge pressure to spike. Visually inspect both service valves and confirm they are fully back-seated (open).

  2. 02

    Failed or disconnected PWM valve coil

    Part replacement

    The PWM expansion valve coil controls refrigerant metering into the system. A burned-out coil or a loose, corroded connector can prevent the valve from opening properly, starving the suction side and driving up the compression ratio. Inspect the connector for damage and test the coil for continuity.

  3. 03

    Low refrigerant charge

    Part replacement

    Insufficient refrigerant in the system lowers suction pressure while discharge pressure remains elevated, pushing the compression ratio above 8.5. This condition typically accompanies a slow leak somewhere in the refrigerant circuit and requires leak detection followed by recharge.

  4. 04

    Blocked or dirty outdoor coil

    Wiring / connection

    Heavy debris, dirt, or ice buildup on the outdoor condenser coil restricts airflow, causing condenser pressure to rise and increasing the compression ratio. Inspect and clean the outdoor coil and verify that airflow around the unit is unobstructed.

  5. 05

    Non-condensables or contaminants in refrigerant circuit

    Part replacement

    Air or moisture introduced into the refrigerant circuit raises head pressure disproportionately, which elevates the compression ratio. This typically requires recovering the refrigerant, evacuating the system, and recharging with clean refrigerant.

See the test procedure for each cause

Frequently asked questions about P428

What does P428 mean on a Samsung air_conditioner?
P428 indicates that the compression ratio on outdoor unit compressor 1 has exceeded 8.5 and held that level for 5 consecutive minutes. This ratio is calculated from discharge pressure versus suction pressure, and a reading this high means the compressor is under abnormal stress. The error is designed to protect the compressor from damage caused by sustained operation outside safe pressure limits.
Can I fix P428 myself, or do I need a technician?
One check a homeowner can safely perform is confirming that the outdoor unit is not blocked by debris and has adequate airflow clearance. However, most of the root causes, including checking service valves, testing the PWM valve coil, and verifying refrigerant charge, require technical knowledge and, in the case of refrigerant handling, EPA certification. It is strongly recommended to have a qualified HVAC technician complete the diagnosis and repair.
Is it safe to keep running the air conditioner with a P428 error?
Continuing to operate the unit with P428 active is not advisable. A sustained compression ratio above 8.5 places extreme mechanical and thermal stress on the compressor. Prolonged operation in this state can cause permanent compressor failure, which is a significantly more expensive repair than addressing the underlying cause early.
Will resetting the unit clear the P428 error?
A power reset may temporarily clear the fault code, but if the underlying condition, such as a closed service valve, a faulty PWM valve, or low refrigerant, has not been corrected, the error will return once the compression ratio exceeds 8.5 again for 5 minutes. Resetting without diagnosis and repair is not a solution and risks compressor damage.
How much does it cost to repair a Samsung air conditioner showing P428?
Repair costs depend heavily on the root cause. Correcting a closed service valve or cleaning a blocked coil is relatively inexpensive, typically in the range of $75 to $200 for a service call. Replacing a PWM valve coil or recharging refrigerant after a leak repair can run $200 to $600 or more. If the compressor has already sustained damage, replacement costs can range from $800 to well over $2,000 depending on the unit.

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