How to Check a Furnace Limit Switch
Introduction:
A furnace limit switch is a crucial component of a heating system that ensures the safe operation of the furnace. It is designed to shut off the furnace if the temperature inside the unit exceeds a certain threshold. Overheating can lead to serious damage to the furnace and even pose a fire hazard. Therefore, it is essential to regularly check the furnace limit switch to ensure its proper functioning. In this article, we will guide you through the process of checking a furnace limit switch.
Step 1: Turn off the Power Supply
Before checking the furnace limit switch, it is important to ensure your safety. First, turn off the power supply to the furnace at the main electrical panel. This will prevent any electrical shock while inspecting the limit switch.
Step 2: Locate the Limit Switch
The furnace limit switch is usually located near the burners or heat exchanger. It is a small, rectangular device with two copper-colored wires connected to it. The switch may be mounted on the side or back of the furnace.
Step 3: Inspect the Wiring
Carefully inspect the wiring connected to the limit switch. Ensure that the wires are securely fastened and not damaged. Look for any signs of corrosion, loose connections, or exposed wires. If you notice any issues, it is important to repair or replace the wiring before proceeding.
Step 4: Check the Contacts
The limit switch has two contacts, usually labeled as “A” and “B.” Use a multimeter to check the continuity between these contacts. Set the multimeter to the ohms (Ω) setting and touch the probes to the corresponding contacts. If the multimeter reads “OL” (overload) or shows no continuity, it indicates that the switch is not functioning properly.
Step 5: Test the Switch
To test the switch, you can use a hairdryer or a heat gun to gently heat the switch. As you apply heat, observe the switch’s response. If the switch opens (disconnects the circuit), it is working correctly. However, if the switch remains closed, it may be faulty and need to be replaced.
Step 6: Clean the Switch
If you notice any dirt or debris on the limit switch, clean it using a soft cloth or a vacuum cleaner with a brush attachment. A clean switch will ensure proper heat transfer and reduce the risk of overheating.
Step 7: Reset the Switch
After checking and cleaning the switch, you may need to reset it. This process varies depending on the furnace model. Refer to the manufacturer’s manual for instructions on how to reset the limit switch.
Conclusion:
Regularly checking the furnace limit switch is an essential maintenance task to ensure the safe and efficient operation of your heating system. By following the steps outlined in this article, you can easily inspect and maintain your furnace limit switch, preventing potential hazards and extending the lifespan of your furnace. Remember to always prioritize safety when working with electrical appliances and consult a professional if you are unsure about any aspect of the process.
