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10 Simple Steps To Troubleshoot a Furnace Limit Switch

10 Simple Steps To Troubleshoot a Furnace Limit Switch

Nothing is more frustrating than discovering that a malfunctioning limit switch has rendered your furnace system inoperable. Therefore, the item you’ll frequently wonder about is knowing how to cure it. So, stop wondering now! Because the solution is provided below!

You should do the following in order to safely troubleshoot your furnace limit switch:

  1. First, shut off the power to your furnace.
  2. Locate the heating duct for your furnace, and then use a screwdriver to unlock the panel.
  3. Look for the limit switch on the heating duct panel’s top.
  4. Pull the switch’s body to reveal two metal arms, then turn it on.
  5. Check the settings for the components in the center of the two arms.
  6. Identify the settings for each arm.
  7. Set the temperature range for the components to 105 to 115 degrees Fahrenheit.
  8. Set the left arm to 90 degrees and the right to 200 degrees Fahrenheit.
  9. Pull out the white switch to set the furnace to automatic mode.
  10. Utilizing your screwdriver, close the panel before turning on the furnace’s electricity.

That was simple. As we go further into what makes your limit switch trip, keep reading. We’ll also touch on a few common questions individuals have about this topic.

What Leads To Limit Switch Issues?

10 Simple Steps To Troubleshoot a Furnace Limit Switch

A switch can “trip” or abruptly shut down the system for a number of reasons in addition to the switch being malfunctioning. The limit switch, for instance, receives information from a temperature sensor.

When the sensor gets filthy, which can happen in HVAC units, the limit switch may activate.

The furnace’s airflow issues could also cause the switch to trip. Insufficient airflow problems can also develop with blocked furnace filters, tripping the switch.

For the system to function properly and to monitor odd temperature fluctuations in the unit, this device is essential. Therefore, identifying the root of the problem and fixing it right away will assist keep your unit from suffering serious harm.

How Can You Spot A Bad Limit Switch?

While the furnace is running, you should connect a digital voltmeter and test the limit switch’s two networks. The operating standard voltage is 0.1 volts of direct current or less (VDC).

However, your limit switch will probably stop working if the voltage suffered a loss of 0.2 VDC or more. Over time, the contacts may get corroded, broken, or damaged.

The old limit switch can be easily changed or replaced before it seriously harms the device.

How To Tell If A Limit Switch Is Faulty

  • The blowers in your furnace run nonstop.
  • Even if your air conditioner isn’t turned on, it will start blowing cold air.
  • After running for a while, the furnace system unexpectedly shuts off.

Replacing A Furnace Limit Switch

10 Simple Steps To Troubleshoot a Furnace Limit Switch

Due to the evident nature of the limit switch failure symptoms, you might decide against testing your furnace. You might consider simply changing the limit switch as an alternative.

  • Turn off the furnace unit’s electricity.
  • Utilizing a screwdriver, locate the switch’s location and release the access panel.
  • To check if there is any remaining return current, use a multimeter.
  • Before removing the wires, make a note or tape a photo to the switch for future reference.
  • Remove the switch by unscrewing it.
  • Place your new limit switch in place.
  • restored the switch’s mounting plate in a safe manner.
  • Restart the power after covering the panel and doing so.

How Much Does A Limit Switch Replacement Cost?

For your furnace, a limit switch should only be obtained from the same supplier. This component’s price could range from $4 to $25 depending on your original equipment manufacturer.

However, this will undoubtedly change depending on your brand and unit model.

Can The Limit Switch Be Reset?

To reset the furnace limit switch if you have the most recent model, try turning off the power for 30 seconds, then turning it back on.

It’s never a bad idea to engage a heating expert to reset the limit switch for you if, despite your efforts, the furnace continues to shut off.

How Many Limit Switches Are There And How They Function?

Typically, it comprises of a high limit switch and a limit switch for the fan control. By removing the furnace’s cover panel, you may get to these switches.

These switches also feature a mounting plate with a sensor probe attached to it.

Knowing the fundamentals will help you comprehend limit switches’ operation. Below, we’ll go over a few of them:

High Limit

Controls the gas supply to the furnace unit; for example, if the temperature in a furnace goes too high, a high limit switch will take control of the system and cut off the gas supply.

The heat won’t be able to rise as a result of overheating the furnace unit if no air or gas passes through it.

Fan Control Limit

10 Simple Steps To Troubleshoot a Furnace Limit Switch

The blower motor turns on when the fan switch detects a furnace’s internal temperature, distributing warm air throughout the house.

A fan switch does what it says on the tin: it will turn on and shut off the fan when the interior temperature falls below the setpoint.

while the gas flames continue to warm up and ignite.

Typical Limit Switch Types

Electronics Switches

Switches that use electronics or electromechanical technology feature a rotatable high and low setpoint. These switches can provide 24 volts for the gas valve and 120 volts for the fan.

Solid State Switches

Another typical form of switch is a solid-state switch limit, which has a smaller layout and a circular design. Solid-state switches are devoid of any moving parts.

Additionally, an optical detector device detects and switches things using solid-state components including transistors, resistors, and capacitors.

Due to their extended operating lifespan, solid-state gadgets cost more than electromechanical ones.

Can You Interchange Furnace Limit Switches?

Although pressure switches are not the same as furnace limit switches, they are occasionally incorrectly used as such.

Additionally, pressure switches are a system that triggers your furnace to shut off when fluid pressure reaches a predetermined setpoint.

The limit switch is typically located on top of the furnace panels, whereas the pressure limit switch is typically accessible inside the motor chamber.

Can A High Limit Sensor Rod Switch Be Cleaned?

If the flame sensor rod is dusty, you can gently clean it with a steel wool sponge or sandpaper. The high limit switch includes the flame sensor rod, which extends into the plenum to measure temperatures.

You must undo the two screws holding the high limit switch to the plenum box in order to gain access to the flame sensor rod.

To Sum Up

We’ve learnt what makes your furnace’s limit switch trip throughout this essay. Additionally, you now know how to identify problematic parts and replace them.

Additionally, we covered how to shield your furnace unit from this potential danger to your HVAC system. We sincerely hope that learning this information will change the way you maintain your HVAC system for the better.

10 Simple Steps To Troubleshoot a Furnace Limit Switch

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Written by HVAC Contributor

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