Samsung Air Conditioner Error Code P4

P4 indicates a reverse phase or open phase error on the 3-phase electrical supply. The unit has detected that the three power lines are either connected in the wrong sequence or that one or more phases are missing entirely. The system shuts down automatically to protect the compressor from running on an incorrect or incomplete power supply.

No. The unit will not operate while P4 is active because it has already shut down to protect the compressor. Attempting to override or bypass the fault protection is not recommended. Running a 3-phase compressor on an open phase or in reverse rotation can cause severe mechanical damage and creates a fire or electrical hazard.

Cost depends entirely on the root cause. If the issue is a tripped breaker, a loose terminal, or a reversed phase connection, an electrician service call typically ranges from $100 to $300. If the utility supply is at fault, there may be no charge from the utility. In the rare case that the internal phase detection or control board has failed, parts and labor can range from $300 to $800 or more depending on the unit model and board availability.

Diagnosing and correcting a P4 error involves working directly with 3-phase line voltage, which is hazardous and should only be performed by a licensed electrician or qualified HVAC technician. The first step is measuring voltage across all three phase pairs at the unit's terminal block. If a phase is missing, the fault lies upstream in the breaker panel or disconnect. If the phase sequence is reversed, swapping two supply conductors at the disconnect will resolve it.

A power reset will temporarily clear the fault display, but the P4 code will return immediately when the unit restarts if the underlying supply problem has not been corrected. The phase detection circuit checks supply conditions on every startup. The fault will only stay cleared after the phase sequence is confirmed correct and all three phases show proper voltage.