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Error code reference

Samsung Air Conditioner Error Code P420

High pressure protection control

Samsung codesSamsung air conditioner codes

High pressure protection control – high pressure sensor value over 28 kg/cm²G.

First step from the service manual

Check if all service valves are open; 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 P420 means on a Samsung air conditioner

The P420 error code on a Samsung air conditioner indicates a high pressure protection event triggered when the high pressure sensor detects refrigerant pressure exceeding 28 kg/cm²G on the high side of the refrigerant circuit. This is a safety shutoff condition: the system halts compressor operation to prevent mechanical damage to the compressor, refrigerant lines, and related components. The high pressure sensor continuously monitors discharge pressure, and when readings climb above this threshold, the control board activates protection mode and displays P420.

Excessive high-side pressure typically results from restricted refrigerant flow on the discharge side of the system. Closed or partially closed service valves are the most immediate culprits, as they block refrigerant circulation and cause pressure to build rapidly. A faulty or stuck PWM (pulse width modulation) expansion valve is another primary suspect: if the valve coil fails or the connector loses continuity, the valve cannot modulate refrigerant flow correctly, causing pressure spikes. The diagnostic process should start with verifying all service valves are fully open, then inspecting the PWM valve coil for proper resistance and checking the connector for corrosion, bent pins, or loose fit.

Additional causes can include a dirty or blocked condenser coil reducing heat rejection, non-condensable gases in the refrigerant circuit, refrigerant overcharge, or a failing high pressure sensor producing false high readings. If valve positions and electrical connections check out correctly, a technician should verify sensor output values against known-good reference data and inspect the condenser for airflow obstructions before proceeding to refrigerant circuit diagnostics.

Source: manufacturer service documentation.

Common causes of P420

  1. 01

    Closed or partially closed service valve

    Wiring / connection

    If a service valve on the refrigerant lines was not fully opened after installation or maintenance, refrigerant cannot circulate freely and pressure builds quickly on the high side. Visually inspect all service valves and confirm they are fully open.

  2. 02

    Faulty PWM expansion valve coil or connector

    Part replacement

    A failed PWM valve coil or a loose, corroded connector prevents the expansion valve from regulating refrigerant flow, causing high-side pressure to spike. Check the coil for correct resistance and inspect the connector for damage or poor contact.

  3. 03

    Blocked or dirty condenser coil

    Wiring / connection

    When the outdoor condenser coil is heavily fouled with dirt, debris, or vegetation, heat rejection is reduced and discharge pressure rises. Inspect the coil surface and clean it thoroughly if airflow is restricted.

  4. 04

    Refrigerant overcharge

    Wiring / connection

    Too much refrigerant in the system raises high-side pressure above safe operating limits and can trigger the P420 protection threshold. A technician should measure refrigerant charge using manifold gauges and recover excess refrigerant if needed.

  5. 05

    Faulty high pressure sensor

    Part replacement

    If the high pressure sensor itself is malfunctioning, it may report falsely elevated pressure values even when actual system pressure is within normal range. This can be diagnosed by comparing sensor output to manifold gauge readings.

See the test procedure for each cause

Frequently asked questions about P420

What does P420 mean on a Samsung air conditioner?
P420 is a high pressure protection code that activates when the high pressure sensor detects refrigerant pressure exceeding 28 kg/cm²G on the discharge side of the system. The unit shuts down automatically to prevent compressor and component damage. The fault must be diagnosed and corrected before the system will operate normally again.
Can I fix the P420 error myself?
Some causes, such as a closed service valve or a dirty condenser coil, can be addressed without specialized tools. However, diagnosing the PWM valve coil, checking refrigerant charge, or replacing the high pressure sensor requires refrigerant handling equipment and electrical testing skills. If you are not experienced with HVAC systems, a certified technician should handle this repair.
Is it safe to keep running my air conditioner with a P420 code?
No. The P420 code represents a high pressure condition that can damage the compressor and other refrigerant circuit components if ignored. The unit shuts down as a safety measure, and attempting to override or bypass this protection is not recommended. Address the root cause before resuming operation.
Will resetting the air conditioner clear the P420 error?
A power reset may temporarily clear the displayed code, but if the underlying cause of high pressure is still present, the P420 error will return as soon as the system attempts to operate again. Resetting without resolving the fault can also allow repeated high-pressure events that accelerate wear on the compressor. The cause must be corrected first.
How much does it cost to repair a P420 error on a Samsung air conditioner?
Repair costs vary significantly depending on the cause. Cleaning a condenser coil or opening a service valve is relatively low cost, typically in the range of $75 to $200 for a service call. Replacing a PWM expansion valve coil or a high pressure sensor can range from $150 to $500 or more depending on parts and labor. Refrigerant-related repairs may add to the total if recovery and recharge are required.

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