"always on" furnace fan

I just found this group, and like to search for advices here.
I have moved into this (7-yr old) house for 4 months now, and noticed that the furnace fan is always on. Always blowing. My question is: How do I turn it off?
1) The thermostat is set to auto, but the fan is blowing even if the furnace or the AC is not in operation. 1.1) The AC works when the thermostat is set to COOL. The furnace works when the thermostat is set to HEAT. 2) The fan is still on when I turn the fan switch on the thermostat to OFF. 3) The only way I can turn off the fan is to switch off the furnace itself (by disconnecting the electrical supply). 4) I have a heat return exchange and a humidifier connecting to the system too. These are all off. 5) I have received some advices like: 4.1) That is the way it is supposed to be (!?). 4.2) The relay of the furnace is broken. I cannot find the relay (!) 4.3) The bimetal couple of the furnace needs to be replaced. I cannot locate the couple (!)
Thanks in advance for any help. Minh
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gardin wrote:

Answered your own question. Setting the fan to AUTO should turn it off in the case of the thermostat being shut off. Your question is "why is it still running?"

Is this a four wire hookup to the thermostat? Are any of the wires connecting to the thermostat touching when they shouldn't be? What happens if you disconnect the fan control wire? (I believe it's green) Does the fan continue to run? If it stops, the problem may be in the thermostat. If keeps running, the problem may be in the furnace. Heck, what if you disconnected all the wires to the thermostat?

Isn't always funny? There's always at least one idiot in the bunch. (Reminds me of a clerk at an auto parts store telling me not to use synthetic oil in my car's engine because the pistons will fly off. I tried to get him to explain his logic, but I got bored. But I digress!)

This is what I'm thinking. The relay could be stuck, or somehow it's receiving power.

Eh? I don't think I know enough about furnaces to know what this is. I can think of two possible meanings to this. The bi metal strip is a spiral spring made of two metals that moves at temperature changes. This is inside your thermostat.
Or it could be some sort of thermocouple for sensing residual heat in the furnace, which will keep the blower running for a certain time delay to force the residual heat out of the furnace. This is a possibility that I did not consider. I would investigate how this time delay is hooked up, and disconnect it.
However, thinking about it, would such a sensor be necessary? Wouldn't a furnace simply have a time delay relay? (KISS?) One of the HVAC techs would have to chime in here.

I am not an HVAC person by any means. But in case no one else responds before I do, I hope I can get you on the right track. Is this an electric or fuel type furnace? I only have experience with electric. But I've never had a relay fail, and this is what I would look into. Disconnect the thermostat. --Mike
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The most likely cause of this, is, the fan/limit control (what you refer to as te 'bimetal' thing...) is stuck. It will require a slight adjustment by somone who knows where it is and how to do it properly. For the time being however, if you bang sharply on the side of your furnace about half way up....you will more than likely cause it to become unstuck -- at least temporarily -- and the blower might shut off.
Dave
"Hey....have you hugged your Guage-Manifold today ?!"
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Dave, you never cease to amaze with your bullshit advice. I will admit that you have stopped trying to be the all knowing (who knows nothing) guru, however, might I suggest that you go beat your own head against something hard and sharp...perhaps it will help you too...

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Dave you're such an IDIOT!!
I suppose his furnace has a thermocouple too??
I mean damn you already know it has a fan/limit control! (NOT)
There are several things that could cause the motor to run continuously, are you there to test the different parts?
No, but even if you were, I don't think you could fix it!
~kjpro~
BTW, do you just beat on things you know nothing about and hope for the best?
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Hi Dave, hope you are having a nice day
On 12-Jun-04 At About 21:45:25, Dave HVACowner wrote to All Subject: Re: "always on" furnace fan
DH> From: snipped-for-privacy@webtv.net (Dave HVACowner)
DH> The most likely cause of this, is, the fan/limit control (what you DH> refer to as te 'bimetal' thing...) is stuck.
You have no idea what kind of system he has and just blurt out whatever comes to mind. If you were actually in the trade you would know that most new furnaces use a pcb for fan control.
-=> HvacTech2 <=-
.. "See this? This is a copy; I want you to make me the original."- s.w.
___ TagDude 0.92+[DM] +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ spam protection measure, Please remove the 33 to send e-mail
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Hey...is your name Boyden or Brown???
Dave's Heating & Cooling 869 Glenview Avenue Mundelein, IL 60060
General Information
Original Business Start Date: January 1986 Principal : Mr. David Brown Owner Phone Number: (847) 949-5277 Type-of-Business Classification: Contractors-Air Conditioning/Systems/Repair

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Its Dave Butthead
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CBHVAC posted for all of us....

I thinks it's browneye-because he's an asshole!

--
Tekkie

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Obviously you havnt called a tech, do so because your unit needs regular maintenance to be efficient, and its obviously broke.
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040613 0702 - gardin posted:

You should get the schematic for the system that you have and find out just what turns the blower on and off. Also, you could try disconnecting all of the wires from the thermostat and see if the blower stops running. This would give you at least a clue.
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First, obvious things first....is the AUTO/ON switch set to ON? If so, then move it to AUTO. All the "on" position does is control the fan.

Normal
Normal
Again...check the fan switch...Auto-on...what is it set at? Auto is where is should be.

OK.
Matters none.

Depends...if the original owners wanted this, its possible.

You might not have a relay that you can replace.

Umm...you mean the fan high limit switch....

First of all, NO ONE on the internet can determine for 100% sure with the information you have supplied here what your problem is. We can make wild guesses, some educated ones since at least two of us that have replied to you are actually in the trade...(NOT Dave..hes a wannabe that gies very incorrect and dangerous advice. Take his if you want, but just remember...hes not a pro...not even close to it.)
Depending on the unit you have, you have one, or more of the following wrong, or set wrong....
Thermostat is set to ON, not Auto Fan limit switch settings are too low, or out of adjustment, or the switch, IF your unit has one, is defective. If your unit uses a control board or an ICB as we call it, failure of the board will cause the fan to start and stay on in MOST cases of board failure. You may have an open limit on the furnace, that would tell the ICB that you have had a flame roll out, and many units will default to fan on high when this happens. IF and thats IF your unit uses a relay, for fan control, it may well be defective..or simply stuck. In either case, replacement would be your best bet. If you have a UPG branded unit, you could have something as simple as a blown fuse on the board.
Now...there are other less common reasons for this. You MIGHT have a bad thermostat, but 99% of the time, it wont be the stat. We get calls all the time, and the first thing people tend to replace, WRONGLY is the thermostat. Many times, they fail to mark what wires go where, and end up hooking the new one up wrong and create more issues. You could have a friendly mouse thats found your wiring to the thermostat, chewed on it a bit, and you have a short between the G and R lines...but again...its very rare.
You didnt state what brand, model, or serial number on the unit you have now, so no one can tell if you have a unit that has an ICB or mechanical control that might have failed.
This is a case, where quite simply, you need to have someone there that understands the unit, and can determine what is wrong. In order to do this, all one has to do is open the Yellow Pages, and look under heating and cooling contractors.

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Dave goes to a customers house, Cant figure out the problem , Hits the furnace in anger, It springs to life! 200 buks mam.
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You sure got him pegged!!
~kjpro~
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Stormin and Davey go to a customers house for a call , Stumped and angry after extensive beer diagnosisisisis they kick the dam thing , It Amazingly pops to life, 200 buks mam.
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From what you describe, you need the "fan limit switch" replaced. This isn't a home owner project. It is a relatively easy replacement for a techie who has done this kind of thing. Not killer expensvie, if the techie isn't out for blood.
--

Christopher A. Young
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