Samsung Air Conditioner Error Code P520

The P520 error code on a Samsung air conditioner indicates an outdoor unit Electronic Expansion Valve (EEV) open position self-diagnosis failure, specifically designated as open fault 2. The EEV is a precision refrigerant flow control component that modulates the amount of refrigerant entering the evaporator based on system demand. It is driven by a stepper motor and controlled by the outdoor unit PCB. During self-diagnosis routines, the control board sends drive pulses to move the valve to a fully open position and then verifies the response. If the valve fails to reach or confirm the open position within the expected parameters, P520 is triggered.

This fault differs from a general EEV communication error in that it specifically targets the open-direction travel of the valve. Common root causes include a failed stepper motor coil within the EEV assembly, a damaged or disconnected EEV harness between the valve and the outdoor unit PCB, or a mechanically seized valve that cannot travel to the fully open position. Contamination in the refrigerant circuit or a valve that has been damaged by liquid slugging can also cause mechanical binding.

Diagnosing P520 typically begins with a visual inspection of the EEV wiring harness for damage, corrosion, or loose connections at both the valve and the PCB connector. If wiring checks out, resistance testing of the stepper motor coils can help identify an internal motor failure. A properly functioning EEV stepper motor will show consistent resistance across its coil pairs. If the motor and wiring are both intact, the outdoor PCB itself may be failing to produce the correct drive signal, requiring board-level diagnosis or replacement.