Freezer displays E4 and may stop cooling or run erratically; defrost cycles may not occur properly.

Safety warning: Unplug the freezer before testing any defrost components. The defrost heater operates at line voltage.

Initial inspection:

• Check for heavy frost buildup on the evaporator cover or back wall inside the freezer. Thick ice indicates a defrost system problem.
• Unplug the unit and allow some ice to melt so you can remove the interior rear panel.

Check defrost thermostat and heater:

• Locate components: The defrost thermostat (bi-metal) is clipped to the evaporator tubing; the defrost heater is mounted at the bottom or woven through the evaporator.
• Test continuity: With the freezer still cold (thermostat closed), disconnect the thermostat and measure continuity. It should show continuity when cold. No continuity indicates a failed thermostat.
• Test the defrost heater for continuity. An open circuit means the heater is burned out.

Check defrost thermistor (if present):

• Some Igloo models use a thermistor instead of or in addition to a bi-metal thermostat. Test resistance as with other thermistors; open or shorted readings indicate failure.

Replace faulty parts:

• Install an Igloo-compatible defrost thermostat or thermistor in the same location and orientation.
• Replace a failed defrost heater with the correct wattage and shape for your model. Secure it to the evaporator as originally installed.
• Inspect and repair any burnt or brittle wiring with high-temperature-rated wire and proper connectors.

Reassemble and test: Reinstall the evaporator cover, plug the freezer in, and allow 24 hours of operation. The E4 code should clear and frost buildup should stop increasing.

Note: If all defrost components test good, the main control board may not be initiating defrost and may need replacement.