Samsung Air Conditioner Error Code E428

Error code E428 on a Samsung air conditioner indicates a compressor shutdown triggered by an abnormal compression ratio. Specifically, the system monitors the ratio calculated as (high-side pressure + 1) divided by (low-side pressure + 1), and when this ratio exceeds 8.5 and remains above that threshold for more than 10 consecutive minutes, the controller shuts down the compressor as a protective measure. This ratio is a reliable indicator of pressure balance between the discharge and suction sides of the refrigerant circuit, and a sustained high value points to a significant imbalance in the refrigeration cycle.

The most common source of this imbalance is a restriction or blockage somewhere in the high-pressure side of the system, which causes discharge pressure to climb while suction pressure drops or remains low. Closed or partially closed service valves are a primary suspect, as they can artificially create this pressure differential without any internal system fault. Other causes include refrigerant undercharge, a failing or seized expansion valve, a blocked condenser, or a defective compressor that is not pumping efficiently.

Diagnosis begins by confirming that all service valves are fully open, then comparing the pressure readings from a manifold gauge set against the values reported by the S-net diagnostic interface. If the gauge and S-net readings agree and the ratio is genuinely elevated, the technician should inspect the condenser coil for fouling, evaluate refrigerant charge levels, and assess expansion valve operation. A discrepancy between manifold and S-net values may indicate a faulty pressure sensor rather than an actual refrigerant circuit problem.