How do I adjust the fan limit on my furnace?
- Open up the access panel on the furnace.
- Look for the fan limit control switch encased in a small rectangular box.
- Slide the cover off the control switch or lift it up.
- Set the markers to the appropriate settings for your furnace.
- Pull out the white switch to reset the limit control to automatic.
Full Answer
How do you reset the limit on a Furnace Fan?
Open up the access panel on the furnace. Look for the fan limit control switch encased in a small rectangular box. Slide the cover off the control switch or lift it up. Set the markers to the appropriate settings for your furnace. Pull out the white switch to reset the limit control to automatic.
What temperature can a fan limit be adjusted on a furnace?
An adjustable fan-limit controller typically is designed for furnaces operating at temperatures from 100°F to 250°F, has a FAN OFF lower limit that can be adjusted from 50°F to 200°F, a FAN ON switch adjustable from 65°F to 215°F and a fan HIGH LIMIT stop set at 200°F.
Can you adjust the speed of your Furnace Fan?
If you know what you are doing, it is very simple to adjust the speed of your furnace fan. There are only a few steps required for most units and having the control will allow you to get your unit to give you the service you need. Check out furnace fans on Amazon.
Where is the fan limit control switch on a furnace?
The switch is one of the easier devices and attachments on a furnace. The average consumer can both locate and set the fan limit control switch with ease. Open up the access panel on the furnace. Most slide off or unhook for easy access. Look for the fan limit control switch encased in a small rectangular box.
How do I set fan limit control?
3:044:05How to adjust the Honeywell fan and limit switch - YouTubeYouTubeStart of suggested clipEnd of suggested clipIf you put a below about a hundred degrees this level and stay on all the time especially in theMoreIf you put a below about a hundred degrees this level and stay on all the time especially in the summer. But be sure and keep those things pretty well separate.
Can furnace fan speed be adjusted?
Once you cut the power, you can remove the cover of your furnace to get access to the control board. Adjusting the pulley on the blower driver motor lets you increase or decrease the blower speed.
What should fan limit 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.
How do you reset the fan limit on a furnace?
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.More items...
What fan speed should I use for heat?
To calculate your needed fan airflow for the heating mode of operation, divide the furnace's rated input by 10,000. This will give you the necessary multiplier to obtain the cfm per 10,000 Btu for the gas furnace type you're setting up. Let's say you have a 60,000-Btu input, 90 percent-plus furnace.
How fast should furnace blower?
While most models of furnace fans are capable of moving at 1,200 revolutions per minute (RPM), some spin at a slower rate. For residential furnace installation units, the maximum speed of most fans is typically 1,500 RPMs.
How does a combination fan limit switch works and what should the settings be on the fan off fan on and Highlimit?
1:115:51Troubleshooting the Fan Limit Control Switch on a Furnace, Temperature ...YouTubeStart of suggested clipEnd of suggested clipRight here and as it heats up it starts turning. And as it turns it rotates this dial right hereMoreRight here and as it heats up it starts turning. And as it turns it rotates this dial right here this rotates clockwise. And then when the ignition assembly shuts off it turns counterclockwise.
Where is the furnace limit switch located?
The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off.
Why is my furnace fan blowing constantly?
Some situations that could cause a furnace fan to constantly run include: Using the wrong thermostat setting. The fan limit switch is on the wrong mode. Faulty equipment.
How do you manually reset a limit switch?
That is, it shuts down completely. You can try resetting the furnace limit switch yourself if you have a newer model by turning off the furnace for 30 seconds and then turning it back on.
Where is the high limit reset button?
The High Limit Reset Button is located behind the gas valve.
How do I know if my furnace has a high limit switch?
1:254:00How To Test and Bypass The Upper Limit Switch On Your FurnaceYouTubeStart of suggested clipEnd of suggested clipSet your volt meter on ohms. Take your two probes and touch these two contacts. And if it's good itMoreSet your volt meter on ohms. Take your two probes and touch these two contacts. And if it's good it will say zero. Any other reading then it means this upper limit switch is bad.
What happens if a furnace blower fan fails to start?
If a furnace blower fan fails to start but the furnace heat source (gas or oil fired burner) is running , the heat exchanger would be come overheated and may warp and crack. The fan limit switch is designed to prevent this damage by shutting off the burner if plenum temperatures reach the high limit.
How does a blower fan work?
The blower fan moves warm air into the occupied space. The blower fan draws cool air from the occupied space, through return ducts, pushing that air up through the furnace heat exchanger where it is heated, and onwards through supply ducts to supply registers through which warm air is blown into the occupied area.
Why does my furnace oil burner cycle on and off?
If the furnace oil or gas burner is very high capacity, or if the furnace fan/limit controls have been set to cause this effect, the burner may on some systems cycle on and off periodically while the warm air blower continues to run.
What happens when the thermostat is satisfied?
When the thermostat is "satisfied" - that is when the temperature of room air around the thermostat has reached the thermostat's set temperature - the thermostat will stop calling for heat - by in essence opening or turning "off" the switch that in turn tells the furnace that no more heat is needed (right now).
What is furnace safety circuit?
General note on furnace safety circuits. A number of safety circuits are employed to ensure safe and proper furnace operation. These circuits serve to control any potential safety hazards and serve as inputs in the monitoring and diagnosis of abnormal function.
What does MRLS mean on a furnace?
“MRLS” = “Manual Reset Limit Switch” I apologize, used my own acronym and it won’t happen again. My blower fan is at the top of the furnace, pretty much in its own housing, the Manual Reset Limit Switch is mounted there so it’s in a much lower temperature environment..
What happens if the primary limit control does not work?
If the primary limit control does not function during this test, the cause must be determined and corrected.
Step 1
Open up the access panel on the furnace. Most slide off or unhook for easy access.
Step 2
Look for the fan limit control switch encased in a small rectangular box. It should be located near the top of the furnace within the panel.
Step 3
Slide the cover off the control switch or lift it up. Inside you'll see the switch itself sticking out along with a dial with temperature settings.
Step 4
Set the markers to the appropriate settings for your furnace. Check with your owner's manual for suggested temperatures. 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.
Step 5
Pull out the white switch to reset the limit control to automatic. The blower should respond to the new settings within half an hour.
Hot to Tell if Your Furnace Limit Switch is Bad
Limit switches rarely go bad. But when they do, you’ll experience severe challenges running the furnace. The following are some common symptoms of a bad furnace.
Can You Reset a Limit Switch?
Yes, you can reset a bad limit switch – as long as it’s not defective. It’s a straightforward process, as we’ll see shortly.
Where is the Reset Button on a Limit Switch?
The reset button on the limit switch is located on a panel underneath the furnace’s heating duct. Heating ducts are typically located in the home’s basement or utility closet. In most cases, you need to open the panel (with a screwdriver) to access the duct.
How to Reset a Furnace Limit Switch – Step-by-Step
If you feel that all your limit switch needs is a reset, not a replacement, the following is a step-by-step guide to reset it.
Can I Bypass a Limit Switch?
Yes, you can bypass the furnace limit switch, though we don’t recommend it. Bypassing the limit switch creates a massive fire risk as you’d essentially be running the furnace with no regard for potential overheating. What if the home becomes too hot?
How to Jump a Limit Switch
Jumping is just another word for “bypassing.” To jump your limit switch, disconnect the two wires attaching to the switch and connect them directly.
How Much Does it Cost to Replace a Furnace Limit Switch?
Furnace limit switches cost between $5 and $25. Meanwhile, professional servicing costs $60 to $200, depending on the type of furnace and your geographic location. So, you should be prepared with at least $65 if you prefer a professional replacement.
What Does the Furnace Limit Switch Do?
The furnace limit switch is a relay circuit within the furnace that determines the operational state of the furnace blower. It decides when to turn on the blower and when to turn it off. The on and off switching happens at specified temperatures.
How the Limit Switch Works
When you turn on the furnace, the thermostat sends a signal to the control board that turns on the furnace and initiates the heating process. However, the limit switch doesn’t close immediately.
Do All Furnaces Have a Fan Limit Switch?
Yes, all furnaces have a high limit switch as it’s critical to the operation of the furnace. For one, the limit switch is solely responsible for turning the blower motor on and off. There’s no other way to operate the blower motor.
Where is the Furnace Fan Limit Switch Located?
The furnace fan limit switch is located inside the furnace panel cover, near the upper right corner. To access it, proceed as follows;
How Do I Know if My Fan Limit Switch is Bad?
It’s best to have the limit switch checked during annual furnace fine-tuning. This allows HVAC technicians to fix potential issues in advance for trouble-free heating throughout the winter period. However, you must also continuously watch for signs of trouble whenever you turn on the heater.
How to Bypass the Furnace Fan Limit Switch
If you’re wondering if you can bypass the furnace limit switch, the answer is yes. You can easily remove it from the equation and let the rest of the furnace run without it. However, beware that bypassing the furnace limit switch is dangerous and highly unrecommended.
How to Test a Furnace Fan Limit Switch
An even better way to verify whether your furnace limit switch is working normally is to test it. The ideal type of test depends on the type of limit switch on your furnace.
