Samsung Heat Pump Error Code P4

P4 indicates that the Samsung heat pump outdoor unit has detected either a reversed phase sequence or a missing phase on its 3-phase power supply. The unit shuts down automatically to protect the compressor from running in the wrong direction or operating under a phase loss condition. All three phases, L1(R), L2(S), and L3(T), must be present and in the correct rotational sequence for the unit to operate.

No. The P4 error causes the outdoor unit to shut down as a protective measure, and you should not attempt to force the unit to run while this fault is active. Operating a compressor with a missing phase or reversed phase rotation can cause rapid mechanical failure of the compressor, which is one of the most expensive components in the system. Leave the unit off until the electrical supply issue is resolved.

Repair costs depend heavily on where the fault is located. If the issue is a blown fuse, a loose terminal, or a reversed wire connection, the repair is typically inexpensive, generally in the range of $75 to $250 for a service call and parts. If the fault lies in the main electrical panel or requires an electrician to run new wiring, costs can range from $200 to $800 or more. In the unlikely event that a faulty control board is responsible, board replacement typically adds $300 to $600 in parts and labor.

Diagnosing and correcting a P4 error involves working with high-voltage 3-phase electrical systems, which is hazardous and in most regions requires a licensed electrician or HVAC technician. A technician will use a 3-phase tester to measure each phase pair and confirm the correct rotation sequence. If the cause is a reversed connection in the disconnect or at the unit terminals, the fix can be straightforward, but it must be performed by a qualified professional with the power isolated first.

A power reset may temporarily clear the P4 code, but the error will return immediately if the underlying electrical problem has not been corrected. Because P4 is caused by a fault in the incoming power supply rather than a sensor or software issue, resetting the unit without fixing the phase problem provides no lasting benefit and risks further damage to the compressor.