LG Hvac Error Code 43

Error code 43 on an LG HVAC system indicates that the high pressure switch has opened due to refrigerant pressure exceeding 600 PSI on the high side of the refrigerant circuit. The high pressure switch is a safety device wired into the compressor control circuit. When pressure climbs past the switch's rated cutout point, it opens the circuit and shuts down the compressor to prevent mechanical damage. This is a protective response, not a component failure in itself, meaning the underlying condition that drove pressure above 600 PSI must be identified and corrected.

The most frequent causes of excessive high-side pressure involve restricted heat rejection. If the outdoor condenser coil is blocked by dirt, debris, or vegetation, heat cannot transfer out of the refrigerant efficiently, causing pressure to climb. Similarly, a failed or slow condenser fan motor reduces airflow across the coil and produces the same result. Refrigerant overcharge is another significant contributor: too much refrigerant in the system raises both suction and discharge pressures, and even a moderate overcharge can push high-side pressure into fault territory under warm ambient conditions.

Non-condensable gases such as air or nitrogen trapped in the refrigerant circuit also elevate high-side pressure disproportionately. A restricted liquid line or a failing expansion valve that does not meter refrigerant correctly can also contribute. Once the root cause is addressed, the switch may reset automatically as pressure drops, or it may require a manual reset depending on the specific switch type installed in the unit. Technicians should always measure actual high-side pressure with a manifold gauge set before assuming the switch itself is faulty.