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Error code reference

Samsung Air Conditioner Error Code 428

Compressor down by compression ratio control

Samsung codesSamsung air conditioner codes

Compressor down by compression ratio control - ratio of (high pressure+1)/(low pressure+1) over 8.5 for more than 10 minutes.

First step from the service manual

Check if service valve is open; compare manifold gauge and S-net values; check indoor/outdoor EEV operation; check for piping clogs; check refrigerant amount.

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

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
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What 428 means on a Samsung air conditioner

Samsung error code 428 indicates a compressor shutdown triggered by compression ratio control logic. The system continuously monitors the ratio of (high-side pressure + 1) divided by (low-side pressure + 1). When this calculated ratio exceeds 8.5 and remains above that threshold for more than 10 consecutive minutes, the control board commands the compressor to shut down as a protective measure. This ratio reflects the pressure differential between the discharge and suction sides of the refrigeration circuit, and an abnormally high value signals that the compressor is working far outside its safe operating envelope.

The most common root causes fall into two categories: refrigerant flow restrictions and refrigerant charge problems. On the high-pressure side, a blocked or partially closed service valve, a kinked or obstructed refrigerant line, or a malfunctioning outdoor electronic expansion valve (EEV) can cause discharge pressure to rise abnormally. On the low-pressure side, a restricted indoor EEV, a clogged strainer, or a low refrigerant charge will cause suction pressure to drop, pulling the ratio upward from below. Both conditions push the compression ratio past the 8.5 limit.

Diagnosis requires connecting manifold gauges to the system and comparing those readings against S-net diagnostic values to confirm sensor accuracy. The technician should verify that all service valves are fully open, inspect both the indoor and outdoor EEVs for proper operation and step counts, check refrigerant piping for restrictions or kinks, and assess the total refrigerant charge. A refrigerant undercharge is a particularly common culprit and will produce low suction pressure alongside relatively elevated discharge pressure.

Source: manufacturer service documentation.

Common causes of 428

  1. 01

    Low refrigerant charge

    Wiring / connection

    Insufficient refrigerant causes suction pressure to drop sharply while discharge pressure remains elevated, easily pushing the compression ratio above 8.5. Verify by attaching manifold gauges and comparing readings to the unit's rated operating pressures.

  2. 02

    Closed or partially open service valve

    Wiring / connection

    A service valve that was not fully opened after installation or maintenance restricts refrigerant flow and skews system pressures. Physically inspect both the liquid and suction line service valves and confirm they are fully back-seated.

  3. 03

    Malfunctioning outdoor or indoor EEV

    Part replacement

    An electronic expansion valve that is stuck closed or operating with incorrect step counts will restrict refrigerant flow and distort the pressure ratio. Check EEV step counts through S-net diagnostics and observe valve response during operation.

  4. 04

    Piping restriction or blockage

    Part replacement

    A kinked refrigerant line, clogged filter drier, or blocked strainer creates an abnormal pressure differential across the circuit. Inspect all accessible refrigerant lines for kinks and check pressure drop across filters or strainers.

  5. 05

    Inaccurate high or low pressure sensor

    Part replacement

    A faulty pressure transducer can report incorrect values that cause the control board to calculate a false compression ratio above 8.5. Compare manifold gauge readings directly against the S-net pressure values to detect sensor drift or failure.

See the test procedure for each cause

Frequently asked questions about 428

What does 428 mean on a Samsung air_conditioner?
Error code 428 means the compressor has been shut down by the system's compression ratio protection logic. The ratio of (high-side pressure + 1) divided by (low-side pressure + 1) exceeded 8.5 and stayed above that level for more than 10 minutes. This indicates an abnormal pressure condition in the refrigerant circuit, most often caused by a refrigerant shortage, a flow restriction, or an expansion valve problem. The compressor is disabled to prevent mechanical damage.
Can I fix Samsung error code 428 myself?
Most of the repairs associated with error 428 require EPA 608 certification to handle refrigerant legally, so a licensed HVAC technician is needed for anything involving the refrigerant circuit. A homeowner can check that the outdoor unit is unobstructed and that any accessible service valves appear fully open, but diagnosing pressure ratios, testing EEV operation, and adding refrigerant must be performed by a qualified technician with manifold gauges and S-net diagnostic tools.
Is it safe to keep running my air conditioner when error 428 appears?
No. The system has already shut the compressor down as a protective response, and attempting to force the unit to continue operating under these conditions risks serious compressor damage. Leave the unit off and contact a technician promptly. Running the system with an abnormal compression ratio can cause refrigerant flooding, overheating, or compressor failure, all of which are significantly more expensive to repair than the underlying cause of the error.
Will resetting the unit clear error code 428?
A power reset may temporarily clear the error and allow the compressor to restart, but the fault will return if the underlying pressure issue is not resolved. Because the shutdown requires the ratio to exceed 8.5 for more than 10 continuous minutes, the root cause such as low refrigerant, a closed valve, or a failed EEV will reproduce the same condition during the next operating cycle. A reset is useful during diagnosis to observe system behavior, but it is not a fix.
How much does it cost to repair Samsung error code 428?
Repair costs vary widely depending on the cause. A simple service valve adjustment or refrigerant recharge typically runs between $150 and $400 including the diagnostic visit. If an indoor or outdoor EEV needs replacement, costs generally range from $300 to $700 or more depending on parts availability and labor rates. A full refrigerant leak repair with recharge can add to those figures. Getting a diagnostic from a certified technician is the best way to obtain an accurate estimate for your specific situation.

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