Thick sheet of ice forming on the evaporator cover or behind the rear interior panel.

Safety warning: Unplug the freezer before accessing the evaporator and electrical components. The defrost heater is high voltage.

Steps to address heavy evaporator ice:

• Manual defrost: Remove food, unplug the unit, and allow all ice to melt. This may take several hours. Use towels to collect water.
• Access evaporator: Remove the rear interior panel to expose the evaporator coil, defrost heater, and thermostat/sensor.
• Inspect components: Look for broken heater elements, loose wires, or a thermostat that has come off the coil.
• Test heater and thermostat: Use a multimeter to check continuity of the defrost heater and thermostat/thermal fuse. Replace any open components with compatible Costway parts.
• Check defrost sensor: Measure resistance of the defrost NTC sensor and compare to expected values. Replace if out of range.
• Control board: If all defrost components test good, the main control board may not be initiating defrost and should be replaced.

Note: After repair, monitor for several weeks to ensure frost does not return excessively.