Top 5 Reasons Why a Refrigerator Won’t Defrost

There once was a young man whose very first apartment had an old freezer-on-top refrigerator that required manual defrosting from time-to-time. Not being familiar with how to accomplish this and having numerous distractions to keep his mind off this matter, the young man decided to ignore the issue. After about a year or two, the ice build-up nearly filled the entirety of the freezer compartment, leaving only a small opening in the middle. This did not cause much consternation for the young man since he could still store up to two frozen TV dinners at a time in that small opening (his main source of sustenance).

The moral of this story? Progress is a wonderful thing since nearly all modern refrigerators have automatic defrost systems to ensure your freezer compartment never becomes a solid block of ice. Alas, even defrost systems on the highest-end refrigerator models can malfunction, so it’s a good idea to be familiar with how the system is supposed to work and how to fix it if it fails.

How an automatic defrost system works

As part of the refrigeration system to keep the refrigerator compartment a consistently cool temperature of around 40° Fahrenheit (4° Celsius) and the freezer compartment a chillier temperature near 0° Fahrenheit (-18° Celsius), the compressor pumps refrigerant in liquid form into the appliance’s evaporator coils (usually located behind a rear panel in the freezer compartment). Once the liquid refrigerant enters the evaporator coils, it expands into a gas which makes the coils cold.  An evaporator fan motor draws air over the cold evaporator coils then circulates that air through the refrigerator and freezer compartments.

The evaporator coils will collect frost as the air drawn by the fan motor passes over them. Without periodic defrosting, frost or ice can build-up on the coils which can significantly impact air flow and prevent the refrigerator from cooling properly. This is where the appliance’s automatic defrost system comes into play. The basic components in this system include a defrost heater, a defrost thermostat, and a defrost control. Depending on the model, the control may be a defrost timer or a defrost control board. A defrost timer turns the heater on for a duration of about 25 minutes two or three times a day to prevent the evaporator coils from frosting over. A defrost control board will also turn the heater on but will regulate it more efficiently. The defrost thermostat plays its part by monitoring the temperature of the coils; when the temperature drops to a set level, the contacts in the thermostat close and allow voltage to power the heater.

Five reasons for why your defrost system is not working

If the evaporator coils show signs of significant frost or ice build-up, the automatic defrost system is probably malfunctioning. Here are the five more likely reasons why:

  1. Burned out defrost heater – If the defrost heater is unable to “heat up”, it won’t be much good at defrosting. You can often tell that a heater has burned out by checking to see if there is a visible break in the component or any blistering. You can also use a multimeter to test the heater for “continuity” – a continuous electrical path present in the part. If the heater tests negative for continuity, the component is definitely defective.
  2. Malfunctioning defrost thermostat – Since the defrost thermostat determines when the heater will receive voltage, a malfunctioning thermostat can prevent the heater from turning on. As with the heater, you can use a multimeter to test the thermostat for electrical continuity, but you will need to do that at a temperature of 15° Fahrenheit or lower for a proper reading.
  3. Faulty defrost timer – On models with a defrost timer, the timer could fail to advance into the defrost cycle or be able to send voltage to the heater during the cycle. Try slowly advancing the timer dial into the defrost cycle. The compressor should shut off and the heater should turn on. If the timer does not allow voltage to reach the heater or the timer does not advance out of the defrost cycle within 30 minutes, the component should be replaced with a new one.
  4. Defective defrost control board – If your refrigerator uses a defrost control board to control the defrost cycle instead of a timer, the board could be defective. While the control board cannot be easily tested, you can inspect it for signs of burning or a shorted out component.
  5. Failed main control board  – Since the refrigerator’s main control board regulates the power supply to all of the appliance’s components, a failing board may be unable to allow voltage to be sent to the defrost system. Before you replace a main control board, you should rule out the other possible causes.

Keep your refrigerator defrosting with parts from Repair Clinic

Once you’ve determined that it’s a defective heater, thermostat, timer, or control board that has caused your refrigerator’s defrost system to fail, you’ll need to find the specific part that matches your model. That’s where Repair Clinic can help. Enter the full model number of the refrigerator in the Repair Clinic website search bar for a complete list of compatible parts. Use the “Part Category” filter (“Heating Element”) and “Part Title” filter (“Defrost Heater Assembly”) to narrow the list down to ID the exact part that fits your fridge. While Repair Clinic stocks parts for all the top brands in refrigeration, including Whirlpool, GE, Kenmore, LG, Samsung, Frigidaire, and Amana, entering the full model number of your refrigerator will ensure you find the right matching part.

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