Fix Your Furnace Woes! Learn The Simple Steps To Test Limit Switch

An electric furnace limit switch is a critical safety device that prevents the furnace from overheating. It works by cutting off power to the heating elements when the temperature inside the furnace reaches a preset limit. Testing the limit switch regularly is essential to ensure that it is functioning properly and that your furnace is operating safely.

Materials You’ll Need

• Multimeter
• Screwdriver
• Gloves

Safety Precautions

• Always turn off the power to the furnace before starting any work.
• Wear gloves to protect your hands from heat and sharp edges.
• Be careful not to touch any electrical wires or components.

Step-by-Step Instructions

1. Locate the Limit Switch

The limit switch is typically located on the side or back of the furnace. It will have two or three wires connected to it.

2. Disconnect the Wires

Use a screwdriver to disconnect the wires from the limit switch. Be careful not to damage the wires or the terminals.

3. Set the Multimeter to Ohms

Set your multimeter to the ohms setting. This will allow you to measure the electrical resistance of the limit switch.

4. Test the Normally Closed (NC) Contacts

Place one probe of the multimeter on one of the NC terminals and the other probe on the other NC terminal. The multimeter should read a low resistance, indicating that the contacts are closed.

5. Test the Normally Open (NO) Contacts

Place one probe of the multimeter on one of the NO terminals and the other probe on the other NO terminal. The multimeter should read a high resistance, indicating that the contacts are open.

6. Test the Common Terminal

Place one probe of the multimeter on the common terminal and the other probe on each of the NC and NO terminals. The multimeter should read a low resistance, indicating that the common terminal is connected to both sets of contacts.

7. Reassemble the Limit Switch

If all of the tests pass, reassemble the limit switch by connecting the wires to the terminals. Tighten the screws securely.

Resetting the Limit Switch

If the limit switch has tripped, you will need to reset it before the furnace will start working again. To reset the limit switch, simply press the reset button on the switch.

Troubleshooting

• The limit switch is not working. Check the wiring connections and make sure that the wires are not damaged. If the wires are good, then the limit switch may need to be replaced.
• The furnace is overheating. The limit switch may be set too high or it may be faulty. Check the temperature setting on the furnace and make sure that it is not set too high. If the temperature setting is correct, then the limit switch may need to be replaced.
• The furnace is not starting. The limit switch may be tripped or it may be faulty. Check the reset button on the limit switch and make sure that it is not tripped. If the reset button is not tripped, then the limit switch may need to be replaced.

In a nutshell

Testing the electric furnace limit switch is a simple and important task that can help to ensure the safe operation of your furnace. By following these steps, you can easily test the limit switch and make sure that it is functioning properly.

What People Want to Know

Q: How often should I test the limit switch?
A: It is recommended to test the limit switch at least once a year.

Q: What are the signs of a faulty limit switch?
A: The signs of a faulty limit switch include the furnace overheating, the furnace not starting, and the limit switch tripping frequently.

Q: Can I replace the limit switch myself?
A: Yes, you can replace the limit switch yourself if you have some basic electrical skills. However, it is important to follow the manufacturer’s instructions carefully and to take all necessary safety precautions.