Samsung Air Conditioner Error Code P427

Error code P427 on a Samsung air conditioner indicates an outdoor unit reverse phase detection error, specifically classified as a type 3 reverse phase fault. This code relates to the three-phase power supply feeding the outdoor unit. In a properly wired three-phase system, the phases must arrive in the correct sequence (typically L1, L2, L3) for the compressor and outdoor fan motors to rotate in the correct direction. When the control board's phase detection circuit identifies that the incoming power phases are out of sequence, it triggers P427 to protect the compressor from running in reverse, which can cause immediate mechanical damage.

The most common trigger for this fault is incorrect wiring of the three-phase power supply to the outdoor unit, either during initial installation or after electrical service work. Swapping any two of the three live conductors at the disconnect, breaker panel, or unit terminal block will reverse the phase rotation. The outdoor unit's main PCB monitors phase sequence continuously and shuts down operation when a reverse or incorrect phase order is detected. This is a protective function, not a component failure in itself, though it can also be triggered by a faulty phase detection circuit on the control board itself.

To resolve P427, a technician should first verify the phase rotation of the incoming supply using a phase rotation meter at the outdoor unit's terminal block. If the rotation is confirmed to be reversed, swapping any two of the three power conductors (at the disconnect or terminal block) will correct the sequence. If the phase rotation is confirmed correct at the supply but the error persists, the outdoor unit main PCB may have a defective phase detection component and will require board-level diagnosis or replacement.