With the furnace in full operation, connect a digital voltmeter across the two connections of the limit switch. The voltage drop should be less than or a maximum of 0.1 VDC. The switch should be immediately suspect if the voltage drop is 0.2 VDC or higher (Fig. 1 indicates a bad limit switch).
What does a fan limit switch do?
The furnace fan limit switch is designed to activate and deactivate the furnace blower assembly. This component is responsible for transmitting warm air throughout the air ducts in your home. In addition, the furnace limit switch is also engineered to shut down the furnace to ensure it doesn’t overheat.
How do you reset a fan limit switch?
How to Reset a Furnace Limit Switch
Locate your furnace’s heating duct. Locate the white limit switch. Look at each arm to identify the settings. Identify the component (setting) located in between the two arms. Set the temperature on the middle component to approximately 105 to 115 degrees Fahrenheit.
What should my fan limit switch be set at?
For a general guide, set the two lowest ones (from the furthest left) to 100 and 130 degrees to control when the fan comes on and goes off. The third marker should be set around 200 degrees as a safety shut-off for the burner.
Can you bypass a fan limit switch?
Yes, you can bypass the high limit switch for testing.
What is the purpose of a fan switch?
And why is it so important? The switch on your fan reverses the direction of rotation on your fan. So it can spin clockwise or counter clockwise.
Should I run my furnace fan all the time?
Running the furnace fan all the time can help by constantly pulling the cold air from the lower level and warmer air from the upper level, blending the two, and then redistributing a more stable, even temperature throughout the home.
How does a limit switch work on a furnace?
A limit switch is a device that’s located under your furnace’s supply plenum. It reads the temperature of the plenum and waits until it gets appropriately warm. Once the plenum reaches a specific temperature, the limit switch sends a signal to the air handler to begin running and delivering warm air to your home.
Why is my limit switch open?
Limit switch codes
The limit switch shuts off the burner when the temperature exceeds a preset temperature. When the temperature reduces to normal, the burner will come back on. The most common reason for limits to open is a plugged filter or a dirty blower wheel.
How much does it cost to replace a limit switch?
Average Cost of a New Furnace Limit Switch
You will need to buy a high limit switch that is produced by the same manufacturer as your furnace unit. Depending on who your OEM is, this component could roughly cost you anywhere from $4 to $25.
What happens when high limit switch trips?
If the furnace high limit switch is tripping, it will wear out at some point. Eventually, it will trigger a lockout mode, and your gas furnace will be unable to operate until the switch is reset or replaced. Make sure you contact your technician to perform this repair task.
Should your furnace fan be on auto or on?
“auto” is the best setting for your furnace fan in the winter. It will aid in saving energy and money while also working to keep your home at an optimal temperature. However, for summer, “on” is the best setting for your furnace fan.
What is a fan limit control?
To put it very simply, the furnace fan limit switch is a control that tells your furnace’s fan when to turn on and off. So, when the furnace isn’t on, it tells the blower not to operate (and send cold air into your home) and when the furnace is on, it tells the blower to turn on and start circulating the warm air.
How much does it cost to replace a limit switch on a furnace?
You’ll need to get a limit switch from the same company that makes your furnace. This component could cost anywhere from $4 to $25, depending on your original equipment manufacturer.
