Wine cooler displays E4 and may stop cooling or run erratically; sometimes accompanied by frost buildup on the evaporator.

Safety warning: Unplug the cooler before accessing the evaporator or control board. The defrost heater and wiring can be live when powered.

Steps to address E4:

• 1. Inspect for frost: Remove interior shelves and the rear panel inside the compartment. If the evaporator coil is encased in solid ice, the defrost system is likely not working.
• 2. 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 from plastic parts. Do not use sharp tools to chip ice.
• 3. Locate the defrost sensor: On many Insignia wine coolers, the defrost sensor is the same or an additional thermistor clipped to the evaporator tubing. Check that it is firmly attached and not broken.
• 4. Check wiring and connectors: Follow the sensor and heater wires to the harness and main control board. Look for burnt connectors, loose plugs, or damaged insulation.
• 5. Test components (advanced):
  • Measure resistance of the defrost thermistor; compare to expected NTC values at the current temperature.
  • Measure resistance of the defrost heater; it should show continuity (typically a few tens of ohms). An open circuit indicates a failed heater.
• 6. Replace failed parts: If the defrost sensor is open/shorted, replace it with the correct Insignia defrost/evaporator sensor. If the heater is open, replace the defrost heater assembly.
• 7. Consider the control board: If both sensor and heater test good, the defrost relay or control logic on the main board may be defective and the board should be replaced.

Note: After repair, reassemble all panels and allow 24 hours for the cooler to return to normal operation.