A fan limit switch is a safety device that is installed in a furnace or other heating appliance. It is designed to prevent the appliance from overheating and causing a fire. The switch uses a bimetallic strip to sense the temperature inside the unit and will shut off the power to the fan when the temperature reaches a certain point. Testing the fan limit switch is an important part of regular maintenance for any heating appliance.
The first step in testing the fan limit switch is to locate the switch. It is typically found near the front of the appliance, near the fan. It will likely be a small, rectangular box with two wires coming out of it.
Once the switch is located, you should turn off the power to the unit. This can be done by turning off the power at the breaker box or unplugging the appliance from the wall. It is important to ensure that the power is completely off before proceeding.
Next, you should remove the switch from the appliance. This can usually be done by unscrewing the two screws that hold the switch in place. Once the switch is removed, you will need to inspect it for any signs of damage, such as rust or corrosion. If the switch is damaged, it should be replaced before continuing.
Once the switch is removed, you can begin testing it. To do this, you will need to use an ohmmeter. This is a device that is used to measure the resistance of electrical components. With the ohmmeter set to the appropriate setting, place one probe on each of the two terminals on the fan limit switch. If the resistance is within the specified range, the switch is working properly. If the resistance is too high or too low, the switch should be replaced.
After testing the fan limit switch, you should reinstall it in the appliance. Make sure to tighten the screws securely so that the switch is held firmly in place. Once the switch is reinstalled, you should turn the power back on and test the appliance to make sure it is working properly.
Testing the fan limit switch is an important part of regular maintenance for any heating appliance. It is a relatively simple procedure and can be done by most homeowners. However, if you are unsure of how to properly test the switch, it is best to consult a professional.