Samsung Air Conditioner Error Code P518

The P518 error code on a Samsung air conditioner indicates that the outdoor unit's discharge temperature has reached a level that triggers protection control for the third discharge temperature sensor or circuit. Discharge temperature refers to the temperature of the refrigerant gas as it exits the compressor before entering the condenser coil. Monitoring this value is critical because excessively high discharge temperatures can damage compressor windings, degrade lubricating oil, and cause refrigerant breakdown. When the discharge temperature climbs beyond the allowable threshold, the control board activates protection mode and displays P518 to prevent permanent compressor damage.

The most common underlying causes include low refrigerant charge, which forces the compressor to work harder and produces abnormally high discharge temperatures, and restricted airflow across the outdoor condenser coil due to debris, dirt buildup, or obstructions. A faulty or mis-reading discharge temperature sensor can also trigger this code even when actual temperatures are within range. Additionally, a failing or overloaded compressor that runs inefficiently will generate excess heat at the discharge port. In some cases, blocked or kinked refrigerant lines and non-condensable gases in the refrigerant circuit can contribute to elevated discharge temperatures.

Diagnosing P518 requires checking the discharge temperature sensor for proper resistance values, inspecting refrigerant pressures with manifold gauges, and verifying that the outdoor coil and fan are operating correctly. Because this fault involves the refrigerant circuit and compressor health, a certified HVAC technician with EPA 608 certification should perform refrigerant-related diagnostics and repairs.