Have you ever had your home’s furnace limit switch tested? It is an important test that must be performed to make sure the furnace is working properly.
If it’s not, you can experience problems like poor ventilation or no heat at all. These problems could be harmful, and in the worst situations, they might cause an electrical fire. The majority of furnaces contain a device in the furnace control board that will alert you when the temperature reaches a certain level.
If you notice that alert sound and the temperature on your thermometer reads extremely hot, you should have this issue looked out for immediately.
This article explains exactly how to test a limit switch on a furnace with a multimeter.
What is a Limit Switch on a Furnace?
An electromechanical device known as a limit switch detects the presence or absence of an object within a specified range of motion. When the lever or plunger of the switch makes contact with an item, it opens a series of contacts, notifying the electronic control circuit to operate.
This safety device prevents the furnace from starting up if it detects an overload or short circuit. Limit switches are essential parts of the automation industry because they act as the main point of contact between mechanical systems and electronic control circuits.
These are simple yet efficient devices that enable machines to recognize and respond to mechanical movements, ensuring reliable and safe functioning.
How do limit switches work?
Limit switches work according to a simple principle. The limit switch activates, signalling the electronic control circuit to take action, when the machine’s mechanical system reaches a particular point in its motion. Depending on the required function, a circuit may be opened or closed by the switch.
When a machine reaches its end position, for instance, a limit switch can be used to detect it and stop it from moving any further and causing damage. In this case, the switch would be designed to activate when the lever or plunger made contact with the machine’s travel limit.
How To Test Furnace Limit Switch With Multimeter
Testing a furnace limit switch with a multimeter is a relatively simple process. Here are the steps you can follow:
Step 1: Turn off the furnace
Before you begin testing the limit switch, make sure the furnace is turned off and the power supply is disconnected.
Step:2. Locate the limit switch
The limit switch is usually located near the furnace blower motor or on the furnace’s heat exchanger. Refer to your furnace’s owner manual or seek guidance from a professional if you are unsure of its location.
Step:3. Remove the wires
Disconnect the wires connected to the limit switch. You can do this by gently pulling the wires from the terminals. Make a note of where each wire is connected to avoid confusion during reinstallation.
Step:4. Set your multimeter
Set your multimeter to measure resistance (ohms). If your multimeter has an auto-ranging feature, it will automatically select the appropriate range.
Step:5. Test the switch
Touch the multimeter leads to the terminals of the limit switch. If the switch is working correctly, the multimeter will display a low resistance reading, usually between 0 and 1 ohm. If the switch is faulty, the multimeter will display an infinite resistance reading, indicating that the circuit is open.
Step:6. Reinstall the wires
If the switch passes the test, reconnect the wires to their respective terminals. If the switch is faulty, it will need to be replaced.
Note: While dealing with electrical appliances, it’s crucial to observe safety precautions. It is advised that you go for expert advice if you are unsure of how to proceed or have any worries.
How Can You Prevent Limit Switches from Failing?
Limit switches are used to stop the flow of a regulated chemical or material, limit switches are utilized. If they are left open, if the pressure is too high, or if the temperature is too high, they might fail.
Limit switches must be installed and maintained correctly if you want to keep them from breaking down. Monitoring pressure and temperature levels is also essential for preventing them from becoming too high.
Conclusion
Limit switches are essential parts of the automation world because they offer a simple and direct but efficient method of detecting and responding to mechanical movements. They have a wide range of forms and applications and are essential for ensuring safe and dependable functioning in several industries.
FAQs
How do I know if my furnace limit switch is bad?
The blower on your furnace running continuously is the most typical indication of a broken limit switch. The limit switch shuts down when the air cools to a specific temperature, just as it prevents the fan from starting until the warm air reaches the proper temperature.
How many ohms should a limit switch for a furnace have?
The switch should reliably go from OPEN to CLOSED each time you touch it, with each closure being 0.1 Ohms or less. Anything more justifies replacement.