Display shows E4; refrigerator may not defrost properly, leading to heavy frost on the evaporator and poor cooling.

Safety first: Disconnect power before accessing the evaporator and electrical components. Use caution around sharp metal and glass heater tubes.

• Check for frost buildup: Remove the freezer rear panel. If the evaporator is encased in solid ice, the defrost system is not working.
• Inspect defrost heater: The defrost heater is usually a glass or metal tube at the bottom or woven through the evaporator. Look for breaks or burn marks.
• Test heater continuity: With a multimeter, measure resistance across the heater terminals. A reading of infinite resistance indicates an open heater that must be replaced.
• Check defrost thermostat/bi-metal: If present, it should show continuity when cold (below freezing). A thermostat that never closes will prevent defrost.
• Temporary manual defrost: To restore cooling temporarily, defrost the evaporator with a hair dryer on low, keeping it moving and away from plastic. Do not use sharp tools to chip ice.
• Replace failed parts: Replace the defrost heater and/or defrost thermostat as needed. If both test good, the main control board defrost relay or logic may be faulty and should be diagnosed by a technician.