You’ve discovered your refrigerator not defrosting. Now what? When you have a refrigerator freezer not defrosting properly, there are some troubleshooting items to check out. Leaving a freezer that won’t defrost for too long may create a bigger problem, so here are some of the most frequent causes for a refrigerator not defrosting.

Common Causes for a Refrigerator Not Defrosting

Defrost Thermostat Defective

The defrost thermostat monitors the temperature of the evaporator coils. During the defrost cycle, the defrost heater liquefies any ice that accumulated on the evaporator coils.

If the defrost thermostat is defective, this process is interrupted, rendering the defrost heater ineffective. To determine if the defrost thermostat is faulty, use a multimeter to test it for continuity when it reaches the low temperature of its operating range.  If it doesn’t have continuity, replace the defrost thermostat.

Defrost Timer Broken

The defrost timer activates the defrost heater frequently throughout the day to ensure the evaporator coils are free from frost.

If the defrost timer isn’t working properly, it may not turn the defrost heater on or advance to the defrost cycle at all. During the defrost cycle, the compressor should turn off and the heater should turn on. You can check to see if this is happening by manually turning the dial to the defrost cycle. If the timer does not activate the defrost components or complete the defrost cycle within 30 minutes, this indicates that the defrost timer is not advancing, and therefore needs to be replaced.

refrigerator won't defrost

Photo Credit: Jarad Brinkerhoff

Defrost Heater Assembly Not Turning On

The defrost heater assembly turns on several times throughout the day to melt away any frost that may have accumulated on the evaporator coils.

If the defrost heater assembly doesn’t work, the entire defrost system will be inoperative, and the evaporator coils will continue to have frost accumulate. Use a multimeter to determine if the defrost heater is working properly. If the defrost heater does not operate continuously, replace it.

Defrost Control Board Failure

The defrost cycle is managed by the defrost control board. The board determines how frequently the defrost cycle needs to run.

If the board is defective, the defrost cycle will never be initiated. However, before jumping to replace the control board, your best bet is to test the defrost heater and defrost thermostat to see if there’s a simple fix. If both the defrost heater and defrost thermostat are fine, then it’s possible the defrost control board needs to be replaced.

If troubleshooting sounds like an overwhelming task, call a licensed service technician to help diagnose and fix the problem right away.