Why is my freezer on but not freezing?

When your residential freezer's interior lights and fans are powered on and running, but the compartment fails to reach sub-zero freezing temperatures, several mechanical or airflow issues are usually at fault. First, inspect the back interior wall of the freezer for heavy frost buildup; if iced over completely, your automatic defrost heater, defrost timer, or defrost thermostat has failed, blocking cold air circulation. Second, check the exterior condenser coils beneath the unit for thick dust blockages. Third, ensure the door is closing tightly. You can troubleshoot internal temperatures using an independent thermometer. You can verify that your corrective action is successful when clearing ice blockages, replacing faulty defrost components, or cleaning condenser coils restores powerful freezing temperatures.