How do I test a defrost thermostat?

A defrost thermostat can be tested for continuity using a multimeter. At normal refrigerator temperatures (below freezing), it should show continuity. If it reads open at cold temperatures, it is likely faulty. Ensure the refrigerator is unplugged before performing any tests.

What causes a defrost thermostat to fail?

Common causes of defrost thermostat failure include electrical shorts, prolonged exposure to extreme temperatures, or general wear and tear over time. It can also fail if the defrost heater or timer malfunctions, leading to incorrect cycling.

Can a faulty defrost thermostat cause my refrigerator to stop cooling?

Yes, a faulty defrost thermostat can prevent the defrost cycle from running, leading to excessive ice buildup on the evaporator coils. This ice acts as an insulator, blocking airflow and heat exchange, which significantly reduces the refrigerator's ability to cool effectively.

Refrigerator Defrost Thermostat Replacement Guide

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[Upgraded] BlueStars 4387503 Refrigerator Bimetal Defrost Thermostat

IMPORTANT: Please check the model number carefully before ordering. If you're unsure about the compatibility, send us your refrigerator model number and we can help you confirm if it fits or not.
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What the 4387503 does

The defrost thermostat monitors the evaporator coil temperature and signals the defrost heater to activate, preventing excessive frost buildup. It ensures the defrost cycle runs only when necessary.

Symptoms when this part fails

Excessive frost buildup in freezer
Refrigerator not cooling adequately
Defrost heater not activating
Water pooling inside or under the refrigerator
Food spoilage due to inconsistent temperatures

Compatibility

Fits the Kenmore family. Specifically:

Any unit originally equipped with OEM part number(s): WP4387503, PS11742474, AP6009317.
Check the model/rating plate inside your appliance and compare it against the fitment table on the product listing before ordering — this guide does not list specific compatible models because Amazon does not provide verified fitment data through this pipeline.

Also replaces: WP4387503, PS11742474, AP6009317

Tools you'll need

Screwdriver set
Nut driver set
Wire strippers
Multimeter
Pliers

Difficulty: Moderate · Time: 30-60 minutes

How to install the 4387503, step by step

Unplug the refrigerator from power.
Empty the freezer compartment.
Remove the freezer back panel to access the evaporator coil.
Locate the defrost thermostat clipped to the evaporator coil tubing.
Disconnect the old thermostat's wires.
Connect the new thermostat, ensuring proper wire connections.
Secure the new thermostat to the coil and reassemble panels.
Restore power and test refrigerator operation.

Related troubleshooting

If swapping this part doesn't fix the issue, check these next:

What is Refrigerator Defrost Mode and How it Works