Freezer shows AL03; display may flash and compressor may not run correctly.

Safety first: Unplug the freezer before removing panels or testing components. Defrost heaters operate at mains voltage.

• Manual defrost: If there is heavy ice buildup on the evaporator, switch off and unplug the freezer. Leave the door open and allow it to defrost completely (use towels to collect water). Do not use knives or heat guns.
• Access evaporator area: Remove the internal rear panel to expose the evaporator, defrost heater, and defrost sensor (NTC). Inspect for broken wires or burnt spots on the heater.
• Check defrost sensor: The defrost NTC is usually clipped to the evaporator tubing. Inspect the connector and wiring. If you have a multimeter, measure resistance; an open circuit or obvious physical damage indicates replacement is needed.
• Check defrost heater (for advanced DIY): With the heater disconnected and freezer unplugged, measure continuity across the heater terminals. Infinite resistance means the heater is open and must be replaced.
• Reassemble and test: After replacing any faulty parts, reassemble the panels, restore power, and clear the alarm via the control panel. Monitor for reoccurrence of AL03 and for normal frost pattern on the evaporator.

If AL03 persists with good heater and sensor, the defrost control circuit on the main PCB is likely faulty and requires professional service.