E12 displayed, unit beeps, ice melts in bin despite compressor operation

Safety: Disconnect power before accessing the evaporator and heater. Components can be sharp and edges may be hot.

Defrost system checks:

• Access evaporator: Remove the interior rear panel to expose the evaporator coil and defrost heater.
• Inspect heater: Look for breaks or burn marks on the Siemens defrost heater. Measure continuity with a multimeter; an open circuit indicates a failed heater.
• Check defrost thermostat: The thermostat or thermal fuse is usually clipped to the evaporator. Test for continuity when the sensor is cold (below freezing). No continuity when cold suggests replacement is needed.
• Control board: If heater and thermostat test good, the main control PCB may not be initiating defrost. This requires further diagnosis and likely board replacement.

Note: Incorrect defrost can cause both excessive frost and warming; ensure all components are correctly reinstalled.