Display shows E4 and the refrigerator may not defrost, leading to heavy frost buildup on the evaporator.

Safety first: Unplug the refrigerator. Use caution around sharp evaporator fins and electrical connections.

Access the defrost components:

• Empty the freezer and remove the rear interior panel to expose the evaporator coil.
• Locate the defrost heater (usually a metal or glass-encased element at the bottom or woven through the evaporator) and the defrost thermostat/thermal fuse clipped to the coil.

• Check for obvious damage: Look for burnt spots, broken heater tubes, or a thermostat that has come loose from the coil.
• Test the defrost heater: With the unit unplugged, disconnect the heater leads and measure resistance. A typical heater will show continuity (a few tens of ohms). Infinite resistance indicates an open heater that must be replaced.
• Test the defrost thermostat: At freezer temperature, the thermostat should show continuity. If it is open when cold, it is defective.
• Replace faulty parts: Install a new Insignia-compatible defrost heater and/or defrost thermostat as needed. Ensure the thermostat is firmly clipped to the evaporator tubing.
• Clear frost: If the coil is heavily iced, carefully melt the ice with a hair dryer on low heat, keeping the dryer away from plastic parts and wiring. Do not use sharp tools to chip ice.
• Reassemble and test: Reinstall the panel, restore power, and monitor for proper defrosting over the next 24–48 hours.

Warning: If the heater and thermostat test good, the main control board may not be sending power to the defrost circuit and may require professional diagnosis and replacement.