LG Air Conditioner Error Code E428

E428 indicates the compressor has shut down due to an abnormal compression ratio or insufficient pressure differential in the refrigerant circuit. Specifically, the system detected a compression ratio below 1.5 for more than 10 minutes, or a differential pressure below 0.4 MPa for more than 10 minutes. This is a protective shutdown designed to prevent compressor damage. The fault requires a pressure and component inspection to resolve.

The system has already shut the compressor down as a protective measure, so the unit will not provide cooling or heating in this state. Attempting to force operation without addressing the fault could damage the compressor, which is the most expensive component in the system. It is best to leave the unit off and have a qualified technician diagnose the problem promptly.

Diagnosis starts with connecting an S-net service tool to read live system data and fault history, combined with manifold gauges to measure actual high-side and low-pressure values. The technician will compare sensor readings against gauge readings to detect any transducer faults, then inspect the 4-way valve and EEV for proper operation. Compressor current draw is also measured to help determine whether the compressor itself is functioning correctly or has internal failure.

Power cycling the unit may temporarily clear the fault display, but the E428 code will return once the unit restarts and the abnormal pressure condition persists again for 10 minutes. The underlying cause must be diagnosed and corrected for the unit to operate reliably. Repeatedly resetting without repair risks damaging the compressor further.

Repair costs vary widely depending on the root cause. A refrigerant recharge or sensor replacement may cost in the range of $150 to $400. A 4-way valve or EEV replacement typically runs $300 to $700 including labor. Compressor replacement, if required, is the most expensive outcome and can range from $800 to $2,000 or more depending on the system size and installation complexity.