Samsung Air Conditioner Error Code E478

E478 indicates a DC-link voltage error in the outdoor unit's inverter circuit. The DC-link bus voltage has gone below 150V or above 410V, which falls outside the safe operating range. Samsung notes this code can appear briefly after a power cut and may clear on its own once stable power returns. If it persists, further diagnosis of the supply voltage and outdoor controller is needed.

No, the unit will typically shut down when E478 is active because operating the compressor outside the safe DC-link voltage range can damage the inverter and compressor motor. Do not attempt to force the unit to run while the error is present. Address the root cause first, whether that is restoring stable power or repairing a faulty component, before putting the system back into service.

Repair cost depends on the root cause. If the fix involves tightening a loose wiring connection or resetting after a power event, costs may be minimal, covering only a service call in the range of $75 to $150. If the outdoor controller board needs replacement, parts and labor typically range from $200 to $600 or more depending on the model and local labor rates. Getting a diagnostic visit first will clarify exactly which component has failed before committing to parts.

A reset can clear E478 if the fault was caused by a temporary power interruption or brief voltage sag, as these conditions resolve once power stabilizes. To reset, power the unit off at the breaker, wait several minutes, then restore power. If the code returns after reset, the underlying cause such as low supply voltage or a faulty outdoor controller board must be addressed before the unit will operate normally.

Start by checking that the incoming AC supply voltage to the outdoor unit is stable and within the rated specification. If a power cut recently occurred, wait for power to fully restore and reset the unit at the breaker. If supply voltage is normal and the error persists, inspect the outdoor controller board for damaged capacitors or other visible component failures. A qualified technician with a multimeter can measure the actual DC-link voltage and confirm whether the board requires repair or replacement.