Refrigerator Auto Defrost Problems

Modern fridges come with Auto Defrost as a standard feature. This feature automatically melts away any ice or frost build-ups inside the fridge, particularly around the evaporator coils. However, the Auto Defrost feature faces its fair share of problems.

Auto Defrost problems are typically related to its defrost timer, heater, defrost thermostat, defrost thermal fuse, or defrost control board. When these components are faulty, the defrost system might turn on for too long or not turn on at all. Both are not good. Excessive defrosting time will damage the fridge and prevent it from cooling down. A lack of defrosting will lead to ice and frost build-ups, affecting the fridge’s efficiency.

To understand the causes behind Auto Defrost problems and their solutions, keep on reading through the following sections!

Why Do Fridges Have An Auto Defrost Feature?

Refrigerators are continuously working at low temperatures to preserve all of the food items inside. As a result, frost and ice often develop on the interior, particularly around colder parts like the evaporator. 

These buildups are not good, as they take up space in the fridge that could otherwise be used to store more items. More importantly, such build ups make your fridge run a lot less efficiently.

To combat this problem, fridges these days automatically defrost themselves once or twice a day for about 25-45 minutes, depending on the brand and fridge model.

Like any other fridge feature, Auto Defrost can fail to work and will require troubleshooting.


Before performing any kind of repair on your refrigerator, always disconnect the appliance from its power supply. That will eliminate the risk of electrocution and lower your overall injury risk. For fridge units connected to a water line, be sure to shut that line as well to prevent spills.

Defrost Timer

The defrost timer is responsible for turning on the Auto Defrost feature at regular intervals throughout the day. When the timer starts the defrost cycle, it will send power to the defrost heater and keep it on for a set period of time.

The heater will generate just enough heat to melt away any frost or ice buildup that has formed around the evaporator coils. Once the defrost cycle has ended, the timer will stop powering the heater and the fridge will resume cooling down as usual.

How it fails:

When a defrost timer is faulty, it will not be able to advance to the defrost cycle. Even if it does, the timer might fail to send power to the defrost heater, which means that none of the frost or ice buildup at the evaporator will melt away.

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How to fix:

Even though the effects of a faulty defrost timer might not seem like a big deal at first, it must be replaced immediately. The regular defrost cycle that happens daily is crucial for the efficient operation of the refrigerator.

Typically, the timer will be located in the fridge’s control housing on its interior.

  • First, remove the housing by unthreading the screws holding it in place and disconnecting any wire harnesses.
  • Next, remove the defrost timer and its electrical connector.
  • Replace it with a new defrost timer, and reconnect the connector the same way as before.
  • Lastly, re-install the control housing inside the refrigerator.
Frigidaire Defrost Timer

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Defrost Heater

The defrost heater is a very straightforward component. It’s a heating element located near or around the evaporator coils. When the defrost timer has entered the Auto Defrost cycle, it will send power to the defrost heater, which will generate heat.

When that happens, all of the ice or frost that has accumulated around the evaporator will melt and flow to the fridge’s drip pan, where it will accumulate and evaporate over time.

How it fails:

Like any heating element, the defrost heater is also prone to failure. The heater could be physically damaged, such as if it suffered a hard impact. Or, it might be an electrical fault, where no power can flow through the heater.

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Either one of those reasons could cause the heater to fail, which means it will not produce any heat and therefore won’t melt away any frost or ice buildup around the evaporator coil.

Related: How to Clean Condenser Coils On a Whirlpool Refrigerator

How to fix:

Unfortunately, a failed defrost heater cannot be repaired. Instead, it must be taken out and replaced. The heater will be located inside the fridge, towards the back. You’ll need to remove the back cover and any wire harnesses attached to it to access the heater.

  • Next, disconnect the heater’s electrical connectors and unmount the heater. The heater might be held in place by mounting screws or aluminium straps.
  • Remove the defrost heater, and replace it with the new one.
  • Mount it in place and reconnect its electrical connector in the same way as the old one.
  • Lastly, replace the back cover and wire harnesses that you removed in the beginning.

Defrost Thermostat

The defrost thermostat is specifically designed to monitor the temperature of the evaporator coils. When it senses that the coils are getting far too cold, the thermostat will allow power to flow to the defrost heater. The heater will then melt away any frost or ice that has likely built up around those coils.

How it fails:

The failed defrost thermostat will not accurately sense the temperature around the evaporator coils. So, even when the coils get far too cold while ice and frost continue to build up around them, the thermostat will fail to allow power to flow to the heater.

Without any power, the heater will not work, and the buildup will gradually worsen.

How to fix:

To fix this problem, you must replace the defrost thermostat that’s located behind the rear panel, inside the fridge.

  • The defrost thermostat will be attached to the refrigerant tubing, close to the evaporator coils.
  • You’ll need to cut the wires connected to the thermostat as close as possible to where they connect to the thermostat.
  • Next, take the new defrost thermostat by connecting the wires. You can use wire nuts to connect those wires effectively and seal the connection with silicone sealant.
  • Lastly, attach the new thermostat to the same spot where you found the old thermostat.
Frigidaire Defrost Thermostat

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Thermal Fuse

The defrost sensor monitors how cold the evaporator is at all times. When the evaporator gets too cold, it will turn on the defrost heater as needed. As a protective mechanism, this sensor also has a thermal fuse attached to it designed to prevent overheating.

How it fails:

If the defrost sensor fails and mistakenly senses that the evaporator is cold even when it’s not, it will continuously send power to the defrost heater. When the heater runs for far too long, it will overheat and cause damage to the fridge.

Thankfully, the thermal fuse is designed to prevent that from happening. When the defrost system overheats, the thermal fuse will blow and disconnect the power supply to the defrost heater.

How to fix:

The thermal fuse is a sacrificial component. That means once it does its job (of blowing and cutting the power supply to the heater), it cannot be reset or repaired. Instead, it must be replaced with a new fuse.

  • This replacement can be done by accessing the defrost system.
  • You can do so by removing the rear panel inside the fridge that covers it.
  • Once there, locate and identify the existing thermal fuse and free it from its electrical connector and anything keeping it strapped in place, such as a zip tie.
  • Next, put the new thermal fuse in place. Then, connect the electrical connector and secure the thermal fuse.

Defrost Control Board

You might already be familiar with the fridge’s primary control board, which coordinates all of the appliance’s functions. The fridge’s defrost system also has a control board of its own with the same purpose.

The board consists of many components and several electrical connectors, all leading to various parts of the defrost system.

The defrost control board coordinates the fridge’s defrost cycles by supplying and disconnecting power to the correct parts as programmed, such as the defrost heater.

How it fails:

There are several reasons why a defrost control board might fail. A short circuit, excess moisture, or even general wear and tear can cause the board to face problems. When it does, it will not be able to carry out the fridge’s Auto Defrost feature successfully.

For instance, the defrost cycle might run too often or for too long each time, preventing the fridge from cooling down. Or, the board might not run the defrost cycle at all, leading to severe ice and frost buildups.

How to fix:

Control boards can’t be fixed, so they must be replaced. You can find yours inside the fridge’s control housing, typically located at the top of the fridge compartment.

  • Once you’ve unscrewed the housing, disconnect any wire harnesses keeping them attached to the fridge.
  • The defrost control board will also have wire harnesses and connectors attached to it. Take a picture of it before you remove anything. You can use the image as a reference later.
  • Once you’ve removed the control board and secured the new one in its place, be sure to reconnect each wire harness the same way as before.
  • Put the control housing back in place, and be sure to reconnect all the necessary electrical connectors.
Whirlpool Defrost Control Board

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Reader Comments (2)

  1. I have a older smaller fridgidare model FRT-045GB , it keep freezing up on coil. There a small white box that has different setting each turn clicks it turns it on turn on. An controls defroster. Ware do I alternate the dial so it operates correctly

  2. I have a problem with my omega refrigerator TM 405P its not defrosting . its cold in the freezer but not cold in fridge compartment not enough cold getting down to the fridge compartment and i can,t find parts for it and a circuit diagram.

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