Display shows E4 and the unit may not defrost properly, leading to ice buildup on the evaporator.

Safety warning: Always disconnect power before working inside the cabinet or near the evaporator and heater wiring.

Steps to address E4:

• Inspect for heavy frost: Remove interior shelves and the rear panel to check the evaporator. If it is encased in ice, the defrost system is likely not working.
• Manually defrost: With the unit unplugged, allow the ice to melt naturally or use a hair dryer on low heat, keeping it at a safe distance to avoid melting plastic. Do not use sharp tools to chip ice.
• Locate the defrost sensor: It is usually clipped to the evaporator tubing near the top or middle. Inspect for damage or dislodging.
• Test the defrost sensor: Disconnect the sensor and measure resistance at a known temperature (e.g., room temperature). Compare to NTC specs. If open or shorted, replace with an Arctic King defrost/evaporator sensor.
• Check defrost heater (if equipped): With the unit unplugged, measure continuity across the defrost heater terminals. No continuity indicates a failed heater that must be replaced.
• Inspect wiring and board: Check connectors from sensor and heater to the main PCB for burning, corrosion, or loose pins.
• Reassemble and test: After replacing any faulty parts, reassemble the interior, restore power, and monitor for normal frost pattern and absence of E4.

Note: If all components test good, the main control board defrost circuit may be defective and require replacement.