Refrigerator Defrost Heater: 4 Signs of Failure, 4 Test Steps and 5 Replacement Steps

What Does the Defrost Heater Do?

The defrost heater melts the frost that builds on the evaporator coils during each defrost cycle. The heater is a metal or glass tube, or a wire element, mounted at or below the coils. The cycle runs at set intervals, and the interval depends on the model. The defrost timer or the control board starts each cycle, and the defrost thermostat ends the heating when the coils are clear. The meltwater drains to a pan under the unit. A failed heater cannot melt the frost, so the coils ice over and the freezer warms. The whole chain of parts is explained in refrigerator frost and defrost problems.

What Are the Signs of a Failed Defrost Heater?

Four signs point to a failed defrost heater.

• Thick frost on the freezer back wall
• Cooling that returns after a manual thaw and then fades again
• A warm freezer while the refrigerator section stays cold
• Frost around the evaporator cover or the vents

A warm freezer has other causes as well, as explained in refrigerator freezer not freezing. Confirm the heater with the test below before buying a part.

What does a failed heater leave behind?

A failed heater leaves frost on the coils and the freezer back wall, which blocks the airflow that cools the freezer. The frost thickens with each cooling cycle.

How do you confirm that frost is the cause?

A manual thaw that restores cooling for a time confirms that frost is the cause. The steps are in refrigerator frost and defrost problems.

How Do You Reach the Defrost Heater?

The defrost heater sits at or below the evaporator coils behind the freezer back panel. The manual shows the panel screws, the cover and the heater location for the model.

Safety notice: Unplug the refrigerator before touching any part behind a panel. Stop at the steps described here. Electrical testing, refrigerant handling and sealed-system work belong to a technician.

1. Unplug the refrigerator and move the food to coolers with ice.
2. Remove the freezer shelves and the ice bin.
3. Remove the screws or clips that hold the back panel.
4. Remove the evaporator cover to expose the coils and the heater.
5. Photograph the heater, the wire positions and the clips before disconnecting anything.

Do not chip ice or use sharp tools near the coils, because a puncture damages the sealed system. Difficulty: easy to moderate for access.

How Is the Defrost Heater Tested?

A technician tests the defrost heater with a meter, and the continuity result is compared with the manufacturer specification. The test steps are technician-supplied. Do not test live circuits at home.

1. Disconnect the heater leads with the refrigerator unplugged.
2. Inspect the heater for breaks, blisters or burn marks.
3. Measure the continuity or the resistance across the heater terminals.
4. Compare the reading with the manufacturer specification for the model.

Record each reading and the specification beside it, because the technician compares the record. Label the leads before disconnecting them, so that the wiring returns to its original positions. Keep the meter probes on the terminal tabs and not on the heater body. A heater that reads sound at room temperature can still fail when hot, so a good reading does not clear the heater if every other part passes.

What does a good heater read?

A good heater shows a continuous circuit and a resistance reading inside the manufacturer specification. The specification differs by model, so no single value applies.

What does a failed heater read?

A failed heater shows an open circuit with no reading, or a reading outside the specification. A broken or blistered element also fails the inspection. Difficulty: technician-assisted.

Why does the order of the tests matter?

The heater is tested first, because a burned-out heater cannot melt the frost and the test is quick. Testing it first can avoid an unnecessary part purchase. Test the other defrost parts only after the heater passes.

What Else Is in the Defrost Circuit?

A heater that tests sound points to the defrost thermostat, the timer or the control board, which are tested in that order. The heater cannot work if a part upstream of it fails.

Is the defrost thermostat at fault?

A failed defrost thermostat can stop the heater from receiving power. A technician tests the thermostat for continuity against the manufacturer specification, at the temperature that the specification states, because the part changes state with temperature. Replace the thermostat if it fails the test. Difficulty: moderate.

Is the timer or the control board at fault?

A failed timer or control board never starts the defrost cycle, so the heater never heats. The board also controls other functions, as explained in refrigerator control board failure signs. Replace the part only after a technician confirms the fault. Difficulty: technician-assisted.

How Is the Defrost Heater Replaced?

Replace a failed heater with the part that matches the refrigerator model number. Use the model-number part list in the manual or from the manufacturer, and compare the new heater with the old one. Five steps complete the replacement:

1. Unplug the refrigerator and photograph the old heater in place.
2. Disconnect the leads and release the clips that hold the heater.
3. Remove the old heater without bending the coils.
4. Install the new heater in the same position and orientation, and secure the clips.
5. Reconnect the leads, refit the cover, the panel and the shelves, and plug in the refrigerator.

Handle the coils gently, because the fins bend easily. Keep the old heater until the repair is confirmed. Allow the refrigerator to cool before returning the food, and watch the freezer back wall for frost over the next weeks. Difficulty: moderate.

When Is It More Than the Heater?

Frost that returns after a new heater points to the thermostat, the control, the door seal or an airflow fault. Check the door seal and the vents first, as explained in refrigerator frost and defrost problems. If the refrigerator is also warm, read refrigerator not cooling. Call a technician for sealed-system faults or for repeated freeze-ups.

What Do People Also Ask About a Refrigerator Defrost Heater?

How do I know if my refrigerator defrost heater is bad?

A thick frost layer on the freezer back wall that returns after a manual thaw points to a failed defrost heater, and a continuity test confirms it.

Can I test a defrost heater with a multimeter?

A continuity or resistance reading across the heater terminals, taken with the refrigerator unplugged, shows whether the heater is intact, and the manufacturer specification confirms the result.

What causes a defrost heater to fail?

Heaters wear out from age and repeated heating cycles, and a failed thermostat or control can also stop the heater from running.

Is a defrost heater replacement worth it?

A heater replacement is a moderate repair that suits most refrigerators, and the repair quote compared with the age of the refrigerator decides.