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Furnace fan What does a fan limiter switch do? When they fail can the fan run continuously?

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Re: furnace fan

What type of system do you have? The auto/on switch on the thermostat will cause the fan to run continuously.

Posted on Nov 04, 2007

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Bryant 340mav036080 limit switch reset time

The primary limit switch in your furnace is an "automatic reset" switch, and should reset itself within a few minutes.

It is a safety device designed to prevent your furnace from overheating. If the furnace does get too hot, the limit switch opens and the burners turn off. The blower should continue to run until the furnace cools down again. The limit switch should then reset itself (usually less than five minutes).

If it will not reset, try tapping on the switch with a screwdriver or other tool. This will often un-stick it. If this does not work, the switch has failed and must be replaced.

A furnace will overheat for many reasons, but the most common are a dirty air filter (should be changed every 1-3 months), or a dirty evaporator coil (only if you also have central air). Make sure everything is clean and all your vents are open to help avoid this problem in the future!

There are other limit switches in the furnace as well, which are "manual reset". They will not reset unless the little red button on them is pressed. If one of these switches opens, it is best to call a contractor to evaluate your furnace, as an unsafe condition may exist.

Mar 02, 2011 | Air Conditioners

1 Answer

I have a 30 year old fedders furnace and the furnace fan runs continuously. I was told by several people that the problem was probably a defective fan limit switch. But because its an older furnace with...

The switch will be the silver/gray box just above the burner in the supply plenum...
There really is nothing you can do to fix that if it is bad... the switch runs off of a bimetal spring and that has just plum worn out...

The main thing you need to check is the insertion depth of the bimetal spring...then you can buy a replacement at any HVAC supply house...

Chances are that what you have is a Honeywell product and you can download anything you need from the honeywell site...

I tell you how to do it in this tip...

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Sep 03, 2010 | Air Conditioners

1 Answer

We have a White-Rodgers 1F80-51. The fan blows

Usually when the furnace blower motor runs all the time
The limit switch or rollout switch is usually open or bad.
The furnace board is seeing that one of those switches is open, so it brings the blower on to try to get the heat out of the combustion chamber area, so the switch will close. But if the switch is bad and won’t close, the furnace board will keep the blower running continuously.

May 31, 2010 | Air Conditioners

1 Answer

We have a Tappah (Model 36c53 type 200) furnace,

If it is an older model unit, there is a switch called a "Fan/Limit" switch. It functions like this: When the burners come on, it heats the switch and fan comes on. If fan fails for any reason, switch continues to heat and then turns everything off as it exceeded a safe limit of temperature.
These are pretty generic and can be purchased from any HVAC shop but most to not sell to the public. You may try W.W. Grainger. They might have one.

Hope this helps

Dec 29, 2009 | Air Conditioners

2 Answers

Goodman a/c blower fan will not shut off

Unhook the thermostat wires on the furnace. If the blower shuts off then your problem is either the thermostat or the thermostat wires. If it contiues to run check you high limit switches next. If all else fails you most likely have a bad blower relay. On most modern furnaces the blower relay is part of the circuit board.
Good luck

Mar 29, 2009 | Goodman CLQ36AR49 Air Conditioner

1 Answer

Urnace fan of some sort runs all the time - set on automatic

If you have it cleaned twice a year they should be able to find this problem. It is one of two thinkgs. There is a limit switch on the fan at the top (inducer) this may be weak and causing the inducer run frequently. The other is there is another limit switch it is a main limit on the fire wall it is also weak and that is why the main blower is running it is trying to cool that limit.

Jan 26, 2009 | Carrier XHB123D X/Y Series Heat/Cool Air...

2 Answers

Fan running but no heat

It could be the circuit board, relay, heat strip coil or limit. If you have the fan switch at the t-stat in auto and the fan is running constantly it's probably a high temp limit that tripped. Was your filter clean or dirty? If you had a dirty filter and/or A/C coil it will restrict air flow and cause the furnace to overheat.

Jan 18, 2009 | Carrier 38CKC042 Air Conditioner

2 Answers

Air conditioner/furnace squirrel cage fan remains running when th

Ensure you don't have a short in your therm wires. Disconnect them, if the furnace continues to run, you have a lockout problem at your furnace. When the motor on the fan fails, it wont run. Check for led codes on the control board. If you don't have led codes, turn off the power to the furnace at the breaker, and watch the unit. If nothing happens, connect the thermostat. If nothing happens still call for heat. Let the therm run through it's cycle, and if the bower runs continuous again, let me know we can walk through that situation.

Dec 05, 2008 | Ruud Central System Air Conditioner

1 Answer

We have a coleman evcon furnace. The furnace runs constantly. It'll get to the temperature but then the fan doesn't quit and it only blows out cool air the the reset switch pops up and needs to be be...

It sounds as if your furnace is exceeding the limit tempperature of the manual reset switch. The coleman is designed for the fan to continually run when this limit switch is tripped in order to keep the heat exchanger cool.( it is a safety feature) afew things may be happening.
1. the manual limit switch( the one you have to push) may be defective.
2. The fan may be running at too low of a speed. Turn power off at circuit breaker. locate circuit board on the board there will be one terminal that says heat if the red wire from the blower is on it tthen you may need to up the speed. follow the wires from the blower to the board if it has multiple speeds then you can isolate the red and put the blue or orange on the heat terminal.
3. the board may have an adjustable fan on and fan off pin selector if it is set up to come on to long or go off to soon it may not be controlling the temp of the heat exchanger properly.
4. I would also suggest checking to see if the orifices and gas valve are set up for your sytem correctly.
these are just simple ideas let me know how things go.

Oct 15, 2008 | Air Conditioners

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