How to Test a Defrost Thermostat

A defrost thermostat is an essential component of a refrigerator that ensures the proper functioning of the defrost system. The defrost system is responsible for removing the frost and ice that accumulates on the evaporator coil, which is the part that cools the air inside the refrigerator. The defrost system consists of three main parts: the defrost timer, the defrost heater, and the defrost thermostat.

The defrost timer is a device that periodically activates the defrost cycle, which usually lasts for about 20 to 30 minutes. During the defrost cycle, the defrost heater is turned on to melt the frost and ice on the evaporator coil. The defrost thermostat is a device that monitors the temperature of the evaporator coil and shuts off the defrost heater when the temperature reaches a certain level, usually between 40°F and 60°F. This prevents the evaporator coil from overheating and damaging the refrigerator.

The defrost thermostat is usually located behind the back panel in the freezer section of the refrigerator, and it is usually clipped onto the evaporator coil. It has two wires that connect to the defrost heater and the defrost timer. The defrost thermostat is a bimetallic switch that opens and closes depending on the temperature. When the temperature is below the set point, the switch is closed and the defrost heater is on. When the temperature is above the set point, the switch is open and the defrost heater is off.

If the defrost thermostat is faulty, it can cause several problems with the refrigerator, such as:

  • Frost and ice buildup on the evaporator coil, which reduces the cooling efficiency and increases the energy consumption of the refrigerator.
  • Poor cooling performance in the refrigerator and freezer sections, which can spoil the food and beverages stored inside.
  • Excessive running of the compressor, which can wear out the motor and increase the noise level of the refrigerator.

Therefore, it is important to test the defrost thermostat regularly and replace it if it is defective. To test the defrost thermostat, you will need the following tools and materials:

  • A multimeter, which is a device that measures electrical resistance, voltage, and current.
  • A pair of wire cutters, which are used to cut the wires of the defrost thermostat.
  • A pair of wire strippers, which are used to strip the insulation of the wires of the defrost thermostat.
  • A pair of needle-nose pliers, which are used to bend and twist the wires of the defrost thermostat.
  • A pair of wire nuts, which are used to connect the wires of the defrost thermostat.
  • A hair dryer, which is used to heat up the defrost thermostat.
  • A bowl of ice water, which is used to cool down the defrost thermostat.

The following are the steps to test the defrost thermostat:

  1. Unplug the refrigerator from the power outlet and remove the food and shelves from the freezer section.
  2. Remove the back panel of the freezer section by unscrewing the screws that hold it in place. You may need to use a screwdriver or a nut driver to do this.
  3. Locate the defrost thermostat, which is usually clipped onto the evaporator coil. It should look like a small, round, metal device with two wires coming out of it.
  4. Cut the wires of the defrost thermostat using the wire cutters. Make sure to leave enough wire length to reconnect them later. You may need to use the needle-nose pliers to hold the wires while cutting them.
  5. Strip about half an inch of insulation from the ends of the wires using the wire strippers. Be careful not to damage the wires or cut yourself.
  6. Set the multimeter to the lowest resistance setting, usually marked as “ohms” or “Ω”. Connect the probes of the multimeter to the wires of the defrost thermostat. The multimeter should display a reading of zero or close to zero, indicating that the switch is closed and the defrost thermostat is working properly. If the multimeter displays a reading of infinity or “OL”, indicating that the switch is open and the defrost thermostat is faulty, you will need to replace it with a new one.
  7. To confirm the test results, you can also heat up and cool down the defrost thermostat using the hair dryer and the bowl of ice water. To heat up the defrost thermostat, hold the hair dryer close to it and turn it on for a few minutes. The multimeter should display a reading of infinity or “OL”, indicating that the switch is open and the defrost thermostat is working properly. To cool down the defrost thermostat, immerse it in the bowl of ice water for a few minutes. The multimeter should display a reading of zero or close to zero, indicating that the switch is closed and the defrost thermostat is working properly. If the multimeter displays the opposite readings, the defrost thermostat is faulty and needs to be replaced.
  8. If the defrost thermostat is working properly, you can reconnect the wires using the wire nuts. Twist the wires together and secure them with the wire nuts. Make sure that the wire nuts are tight and that there are no exposed wires. If the defrost thermostat is faulty, you will need to replace it with a new one that has the same specifications as the old one. You can find the model number and the part number of the defrost thermostat on the label or on the packaging. You can order a new defrost thermostat online or from a local appliance store.
  9. Reattach the defrost thermostat to the evaporator coil using the clip. Make sure that the defrost thermostat is in contact with the coil and that the wires are not touching any other metal parts.
  10. Replace the back panel of the freezer section and secure it with the screws. Put back the food and shelves in the freezer section.
  11. Plug the refrigerator back into the power outlet and check if the defrost system is working properly. You may need to wait for a few hours or a day for the refrigerator to reach the optimal temperature and for the defrost cycle to activate.

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