Freezer not Defrosting: Troubleshooting

Your refrigerator and freezer are designed to work in tandem with each other. Basically, the motor/compressor of the refrigerator directs refrigerant gas through the cooling system and into the evaporator coils of the freezer.

Normally, the ice that forms on the evaporator coils is automatically defrosted a few times a day. If something in the defrost system is not functioning properly, then ice will continue to build up on the coils. When ice builds up, evaporation can not take place, and the freezer and fridge will not stay cool.

There are a few areas to check if your freezer is not defrosting. Most often defrost issues are connected to:

  • The defrost control board
  • The defrost timer
  • The thermostat
  • The Defrost Heater Assembly

Let’s now take a quick look at each of these parts in order to better understand freezer defrost issues.

Issues with the Defrost Control Board

The defrost control board controls the defrost process by starting the defrost cycle. How often the defrost cycle occurs is another job of the defrost control board. If the defrost control board is not functioning properly, then the evaporator coils will not be automatically defrosted, and ice will continue to build up on the coils.

In most refrigerators and freezers, the defrost control board can be found near the back panel of the refrigerator. The other common location of the defrost control board is in a compartment located inside the fridge toward the top. After unplugging the appliance, take a screwdriver and carefully take out the screws. Once you pull down the appropriate panel, you’ll be able to see the defrost control board.

To determine if this is the defective part, it is best to test the defrost heater and the defrost timer. If these are working properly, then the problem most likely resides with the defrost control board. Depending on the year and model of your refrigerator, a new defrost control board can cost between $25.00 and $200.00.

Issues with the Mechanical Defrost Timer

It is common in older more basic fridges to have a mechanical defrost timer. The mechanical defrost timer has the same responsibility as the adaptive control board which is to handle the defrosting process. Basically, the defrost timer turns the heater on for a predetermined amount of time. Typically it runs for about 25 to 30 minutes duration’s, two or three times a day. A defrost timer that needs to be replaced will not advance the system into the defrost cycle or send voltage to the heater.

Depending on the make and model of the refrigerator, you can locate the defrost timer either in the control panel, behind the fridge or behind the kick plate.

To test the defrost timer, remove it after unplugging the refrigerator. You will need to use a screwdriver to advance the dial to the defrost setting. If all is working correctly, the compressor will turn off, and the heater will turn on. If it doesn’t advance out of the defrost cycle within 30 minutes, the piece will need to be replaced. A new replacement defrost timer should cost between $10 and $80.00.

Issues With The Defrost Thermostat

An important part of the defrosting process is the defrost thermostat. The thermostat monitors the temperature of the evaporator coils. When the thermostat is functioning properly, the heater will turn on and defrost the coils. A defective thermostat will cause the coils to remain iced over, and more ice will keep building up until both the fridge and the freezer will lose the ability to stay cool.

Finding the thermostat depends on which type of unit you have. Freezer-on-top models will have the thermostat located either in the back of the unit or underneath it. Side-to-side models will have the thermostat located in the back behind the freezer portion.

To test your thermostat, you’ll need a multimeter to test the continuity of the part. Remove the thermostat from the appliance and place it in a glass of ice water for a few minutes. After rotating the multimeter dial to the least resistance, use the probes to touch the terminals of the thermostat. If the needle doesn’t move or the display does not change, the thermostat will need to be replaced. A new one should cost between $50 and $100.

Issues With The Defrost Heater Assembly

The defrost heater assembly is an important part of the whole defrosting process. This is the part that actually heats up and defrosts the evaporator coils. If this fails, the coils will not be defrosted, and the ice will continue to build up.

To locate the defrost heater assembly, where ever your evaporator coils are in your freezer you will find the defrost heater. To test the heater assembly, remove it and set your multimeter to the ohms setting. Place the probes on the defrost heater terminals. The meter reading should be between zero and infinity. If you get readings of zero or infinity, the defrost heater assembly is defective and should be replaced. A new heater assembly should run about $18 to $80.00.


There are several good reasons to know about the inner workings of your refrigerator and freezer. Firstly, troubleshooting the problems yourself can save you time and money. Also, you will be more aware if you need to call a repair specialist. If you do decided to replace the parts yourself, you’ll have the satisfaction of a job well done.

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