Samsung Air Conditioner Error Code E451

Error code E451 on a Samsung air conditioner indicates a low pressure switch fault detected for the second time in the refrigerant circuit. The low pressure switch is a safety device that monitors suction-side pressure in the refrigerant system. When refrigerant pressure on the low side drops below the switch's minimum threshold, the switch opens and triggers a fault. The "2nd detection" designation means the system has logged this condition on a second consecutive or cumulative detection cycle, indicating a persistent or recurring low pressure condition rather than a transient anomaly.

Low pressure faults typically point to issues within the refrigerant circuit or components that affect refrigerant flow and volume. A loss of refrigerant charge due to a leak is one of the most frequent underlying causes, as reduced refrigerant mass lowers suction pressure. Restrictions in the refrigerant circuit, such as a clogged filter drier or a partially closed or faulty expansion valve, can also starve the compressor of adequate refrigerant flow and cause suction pressure to fall. Additionally, a malfunctioning or failed low pressure switch itself may send a false open signal to the control board even when actual pressure is within acceptable range.

Because this is a second-detection fault, the system has already attempted to recover from an initial low pressure event and has determined the condition is not self-resolving. This typically causes the unit to lock out compressor operation to prevent compressor damage from running under a deep vacuum or with insufficient refrigerant lubrication. A thorough diagnosis should include measuring actual suction-side pressure with manifold gauges, inspecting for refrigerant leaks, and testing the switch continuity.