The furnace fan limit switch, an important safety device found in most furnaces, helps regulate the temperature of the furnace and prevents it from overheating.
This switch is typically located near the heat exchanger and is crucial for controlling the operation of the blower fan. It is essential to understand whether your furnace fan is on or auto in winter.
Setting it to “on” means the fan runs continuously, which can help distribute heat more evenly but may increase energy consumption. On the other hand, selecting “auto” allows the fan to operate only when the furnace is actively heating the air. Awareness of the furnace fan setting in winter can aid in troubleshooting and optimizing energy efficiency.
What Does The Furnace Fan Limit Switch Do?
The fan limit switch has two essential functions:
- It turns the furnace blower fan on and off based on the temperature in the furnace. When the temperature rises to a certain point, the switch turns the fan on to draw cool air through the furnace. This cools down the furnace components.
- It shuts down the furnace burner if the temperature gets too high. This prevents damage from overheating.
So, in summary, it controls the blower fan to regulate temperature and acts as a safety shut-off if the furnace overheats.
Where Is The Fan Limit Switch Located?
The location of the fan limit switch depends on the type of furnace you have:
1. Upflow Furnaces
In an up-flow furnace, the fan limit switch is typically located near the motor at the bottom of the blower compartment. It has a small dial on it with temperature settings.
To access it, you’ll need to remove the blower compartment door. This is usually located on the bottom of the furnace. The switch will be mounted to the blower housing or a bracket.
2. Downflow Furnaces
The fan limit switch is located at the top of the blower compartment on a downflow furnace. You’ll need to remove the panel on the side of the furnace cabinet to access the blower section. Then, look at the top of the blower housing for the switch.
3. Horizontal Furnaces
The switch is usually mounted on the back side of the blower compartment for horizontal flow furnaces. Remove the front panel and look towards the back for the fan limit switch.
It’s often located near the motor and blower wheel housing.
Identifying The Fan Limit Switch
To determine the fan limit switch, look for:
- A small dial with temperature settings, usually from 100 to 300 degrees Fahrenheit
- Two terminals for wiring connections
- A manufacturer’s label that says “Fan Limit Control.”
It may also have one to three buttons for manual fan control. The switch is usually a different shape and style than the other controls in the furnace.
Testing The Fan Limit Switch
If you think the fan limit switch is faulty, you can test it:
- Set a multimeter to the RX1 scale and touch the probes to the switch terminals.
- Turn the temperature dial slowly and check for continuity.
- There should only be continuity once the dial passes the minimum set temperature.
- The switch needs replacement if you get continuity at lower temperatures or no continuity at higher temperatures.
Always turn off the power to the furnace before testing the switch for safety.
Replacing a Faulty Fan Limit Switch
If the switch tests faulty or isn’t switching the fan on at the correct temperature, replace it with an identical model:
- Turn off the power to the furnace at the breaker.
- Remove the electrical wires from the faulty switch.
- Unscrew the mounting screws and remove the switch.
- Install the new switch in the same orientation.
- Attach the wires to the same terminals.
- Adjust the temperature dial to the same setting.
- Turn the power back on and test the operation.
Consult the furnace manufacturer’s instructions for proper switch settings and installation. Replacing the fan limit switch yourself can save on costly service calls.
5 Key Facts About the Fan Limit Switch
To summarize critical details about the furnace fan limit switch:
- It regulates blower fan operation based on temperature. The switch turns the fan on and off to control the furnace heat.
- The switch helps prevent furnace overheating. If the temperature rises too high, it shuts off the burner.
- The location depends on the furnace configuration. It’s typically found at the top or bottom of the blower compartment.
- A faulty switch can be tested with a multimeter. Check for improper continuity at different temperatures.
- Always replace the switch with an identical model. Be sure to adjust the new switch to the same temperature settings.
Frequently Asked Questions
Q: Why does my furnace blower run all the time?
A: If the fan limit switch is faulty, it may fail to shut the blower fan off when the temperature drops. This causes continuous blower operation.
Q: My house isn’t heating up properly. Could it be the fan limit switch?
A: If the switch isn’t triggering the blower at the correct temperature, it can interrupt air circulation and cause poor heating.
Q: How do I know if my fan limit switch is bad?
A: Test it with a multimeter. Improper continuity at different temperatures indicates a faulty switch needing replacement.
Q: Does the fan limit switch control the AC as well?
A: No, it only controls the blower fan and burner operation based on furnace temperature. Separate controls operate the AC components.
Q: Where can I buy a replacement fan limit switch?
A: Check with HVAC suppliers for a match for your furnace make and model. Hardware stores may have universal switches.
Conclusion
Knowing where the furnace fan limit switch is located and how it operates helps troubleshoot furnace issues. Upflow, downflow, and horizontal furnaces have different switch locations, but checking the blower housing is a good starting point. Testing and replacing the switch may restore regular operation if the blower fan or heating acts up. If you’re wondering why the light is flashing on your Shark battery, understanding this overview of fan limit switch functions and locations will help you maintain furnace safety and efficiency better and shed light on potential issues with your Shark battery
