Furnance fan runs constantly -

Reply

  #1  
Old 07-17-06, 07:01 AM
Member
Thread Starter
Join Date: Nov 2005
Posts: 94
Received 0 Votes on 0 Posts
Furnance fan runs constantly -

My furnance fan runs constantly - The only way for me to shut it off...is by turning off the main power switch to my furnace (itself) -

However as soon as I turn this power switch back on the fan will start right back up (never goes off) -

My AC is central air which runs through my system - It is hot here in Carolina's right now - So it is a pain to have to go the basement every time I want to turn my AC on or off -

My furnace is less then 4 years old -

My first thought would be my fan is shot.....(but then I would think it wouldn't run....not run all the time).

Thanks for any advice -
 
Sponsored Links
  #2  
Old 07-17-06, 01:49 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,485
Received 28 Votes on 22 Posts
Does the fan also run continuously when in the heating mode? If so then it may be a problem with the logic board in the furnace.

On the other hand it could be a thermostat problem. Is the fan switch on the thermostat set to Auto or is it On? (It should be in Auto if you prefer the fan to start and stop with the A/C). Have you replaced the original thermostat?

It may be that the original installer connected the fan for continuous operation when in the cooling mode. As long as the actual A/C system is not sub-cooling the house this continuous operation may help with lowering humidity levels.

Constant fan operation may increase comfort levels by lessening temperature swings and will also do a better job of clearing dust and dirt from the air providing you have adequate filters in the system.

You may have a switch on the furnace itself that allows continuous fan operation, have you looked for such a switch?
 
  #3  
Old 07-17-06, 05:07 PM
Member
Thread Starter
Join Date: Nov 2005
Posts: 94
Received 0 Votes on 0 Posts
Originally Posted by furd
Does the fan also run continuously when in the heating mode? If so then it may be a problem with the logic board in the furnace.

On the other hand it could be a thermostat problem. Is the fan switch on the thermostat set to Auto or is it On? (It should be in Auto if you prefer the fan to start and stop with the A/C). Have you replaced the original thermostat?

It may be that the original installer connected the fan for continuous operation when in the cooling mode. As long as the actual A/C system is not sub-cooling the house this continuous operation may help with lowering humidity levels.

Constant fan operation may increase comfort levels by lessening temperature swings and will also do a better job of clearing dust and dirt from the air providing you have adequate filters in the system.

You may have a switch on the furnace itself that allows continuous fan operation, have you looked for such a switch?
Thanks for the comments -

1. As for my T-stat....yes I have replaced it (a neighbor who runs an AC/heating business came by and did it actually) -

I have the T-stat / fan set for Auto (not "on"). So the T-stat does not seem to be the problem (appears not to be I should say).


2. My logic board on my furnace has a indicator light....which says it is operating fine??? (meaning the red light signals there are no problems?) - This possibly could be not working correclty as well though I assume?

3. I moved into this home last Nov - And when using "heat" I did not have this problem of the fan coming constantly on - It has only happened since I turned the AC on -

However now the fan runs constantly even when the T-stat is shut to OFF (no AC....no heat). Meaning unless I shut down the master switch to my furnace in the basement the fan will constantly be running.

I haven't tried to turn my heat back on though...and see what that does to the fan?...perhaps I should try that.

4. Perhaps you are correct in that the original installer connected the fan for constant "on" when in cooling mode?....however that really wouldn't explain my fan constantly runnning now even when the T-stat is turned to "off"....would it?


Thanks again.
 
  #4  
Old 07-17-06, 06:11 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,485
Received 28 Votes on 22 Posts
Not knowing the specific wiring of your thermostat or furnace I can only guess. I did look at the wiring diagram inside the blower compartment of my Lennox furnace (for some reason I cannot find either the instructions/wiring diagram for the furnace OR my thermostat) and all I can say is to try disconnecting the thermostat leads, including any going to the outside condensing unit of the A/C, on the furnace. Be sure and mark them so that you can replace them exactly. Then see if the fan still runs when the blower door is in place and the power on.

If the fan still runs when all of the thermostat (including any leads to the outside condensing unit of the A/C) are disconnected then you have a fault with the logic board. If the blower does not run under these conditions then re-connect the thermostat leads only, leaving the A/C leads disconnected and try again. If the blower then runs (with the thermostat fan switch in AUTO and the system switch OFF) then the problem is in the thermostat or wiring. If the blower does NOT run try switching the fan switch to ON and see if the blower runs. If not then switch the system switch to HEAT and see if the fan runs. If yes then switch to COOL and see if the fan runs (fan switch still in ON) then switch the fan switch to AUTO. The fan may continue to run for a short period of time based on a delay in the thermostat and then stop. If everything checks out fine then re-connect the A/C wiring. If re-connecting the A/C wiring causes the fan to run continuously then the problem is in the outside unit or the connecting wiring.
 
  #5  
Old 07-17-06, 07:43 PM
Member
Thread Starter
Join Date: Nov 2005
Posts: 94
Received 0 Votes on 0 Posts
Originally Posted by furd
Not knowing the specific wiring of your thermostat or furnace I can only guess. I did look at the wiring diagram inside the blower compartment of my Lennox furnace (for some reason I cannot find either the instructions/wiring diagram for the furnace OR my thermostat) and all I can say is to try disconnecting the thermostat leads, including any going to the outside condensing unit of the A/C, on the furnace. Be sure and mark them so that you can replace them exactly. Then see if the fan still runs when the blower door is in place and the power on.

If the fan still runs when all of the thermostat (including any leads to the outside condensing unit of the A/C) are disconnected then you have a fault with the logic board. If the blower does not run under these conditions then re-connect the thermostat leads only, leaving the A/C leads disconnected and try again. If the blower then runs (with the thermostat fan switch in AUTO and the system switch OFF) then the problem is in the thermostat or wiring. If the blower does NOT run try switching the fan switch to ON and see if the blower runs. If not then switch the system switch to HEAT and see if the fan runs. If yes then switch to COOL and see if the fan runs (fan switch still in ON) then switch the fan switch to AUTO. The fan may continue to run for a short period of time based on a delay in the thermostat and then stop. If everything checks out fine then re-connect the A/C wiring. If re-connecting the A/C wiring causes the fan to run continuously then the problem is in the outside unit or the connecting wiring.

Ok - I'll try and test those differing situations -

I will say my AC works fine as is right now - In the sense that it starts up and shuts down when it is suppose to (via the T-stat).

It is the blower/ fan of the furnace that simply stays "on" the entire time (once the furnace is turned on....via the master switch.....regardless if the T-stat is turned on or off).
 
  #6  
Old 07-18-06, 04:45 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 13,936
Received 1 Vote on 1 Post
Constant fan

With the thermostat set to "off" & the fan selector on "auto", try disconnecting the wire to the "G" terminal on the board. Allow up to 5 minutes for the fan to stop. If it does, there is a problem either with the stat or wiring. If the fan does not stop, the problem is probably a stuck relay on the board.
 
  #7  
Old 07-25-06, 11:49 AM
Member
Thread Starter
Join Date: Nov 2005
Posts: 94
Received 0 Votes on 0 Posts
Originally Posted by Grady
With the thermostat set to "off" & the fan selector on "auto", try disconnecting the wire to the "G" terminal on the board. Allow up to 5 minutes for the fan to stop. If it does, there is a problem either with the stat or wiring. If the fan does not stop, the problem is probably a stuck relay on the board.

Ok (I'm really baffled now!!) - I tested like you sugggested (and as another H&C guy told me too) - I removed the green wire that was running to the "G" terminal on my board -

Turn the main switch back on.....Fan comes on immedeitely and runs for 5-10 min.....then goes off (just as you suggested it might).

I then go back to my furnance shut it compeltely down...and restart it....when it restarts...NO fan/blower running! (seems to have narrowed down where the problem is.....right??).

Great - So at that point I look at my bundle of wires running from my T-stat down to my furnace (board)...and there are 3 extra wires (not in use).

Meaning I had a Red, White, Yellow and Green all connected to my board (from the T-stat)......The Green wire was the one going to by "G" terminal.

I also had a black, blue and brown wires that were not being used.

I then took that blue wire that wasn't being used...and hooked it up to both my "G" ternminal on the board....as well as to my T-stat.


Turned my furnance back on......and BAM...fan starts right up again........and I'm right back to the problem of it not turning off??

That leaves me stumped........but then I say to hell with it and disconnect the blue wire from my "G" terminal (just as I had originally done with the green wire that was there).....yet now it makes no differene.....my fan/blower continues to run and won't shut off??

Yet there is no wires connected to the G terminal?


Furthermore my "indicator light" on my 4 year old system suggests everything is fine with the "board" and it doesn't have any problems?


One last thing - On my board there are "five" terminals -

That read

R - C - W - Y - G


Yet I only have 4 wires from my T-stat hooked up? (is this correct??).

I have a Red wire going to R

I have a Yellow wire going to Y

I have a White wire going to W

And a Green (now black) wire going to G

I have nothing from the T-stat going to the "C" terminal....is this correct?

Now there is a wire from my A/C going to that "C" terminal....but nothing from my T-stat.
 

Last edited by meade95; 07-25-06 at 12:29 PM.
  #8  
Old 07-25-06, 02:46 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,485
Received 28 Votes on 22 Posts
Originally Posted by meade95
That leaves me stumped........but then I say to hell with it and disconnect the blue wire from my "G" terminal (just as I had originally done with the green wire that was there).....yet now it makes no differene.....my fan/blower continues to run and won't shut off??

Yet there is no wires connected to the G terminal?


Furthermore my "indicator light" on my 4 year old system suggests everything is fine with the "board" and it doesn't have any problems?


One last thing - On my board there are "five" terminals -

That read

R - C - W - Y - G


Yet I only have 4 wires from my T-stat hooked up? (is this correct??).

I have a Red wire going to R

I have a Yellow wire going to Y

I have a White wire going to W

And a Green (now black) wire going to G

I have nothing from the T-stat going to the "C" terminal....is this correct?

Now there is a wire from my A/C going to that "C" terminal....but nothing from my T-stat.
Your particular thermostat may not require the "C" lead if it is powered by internal batteries OR if it does not have a programming feature.

The "R" lead (from the furnace board) is power to the thermostat switching.

The "Y" lead is from the cooling switch in the thermostat. It connects with the "R" lead when in cooling mode the room temperature is above the "setpoint" (desired room temperature set on the thermostat). In the furnace this starts the blower (fan) in the cooling speed. There may be a time delay before the blower starts. The "Y" terminal will also have a wire going to the A/C condenser (outside) unit to start the compressor.

The "W" lead is from the heating switch in the thermostat. It connects with the "R" lead when in heating mode the room temperature is below the setpoint. In the furnace this will initiate the ignition process through main flame and also energize the blower in the heating speed. There is most likely a time delay before the blower starts.

The "G" lead if for manual blower operation from the thermostat. Its only purpose is to allow you to run the blower by placing the fan auto/on switch in the on position where it will connect the "R" lead to the "G" lead and start the fan.


Just because the diagnostic lights on the furnace board does not signal a problem does not mean that the board is A-OK.

It might help if you could supply the make and model of the furnace.
 
  #9  
Old 07-25-06, 02:49 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 13,936
Received 1 Vote on 1 Post
Wires

Unless your thermostat requires a common for some reason (such as a light), having only a wire to the outdoor unit from "c" is completely normal.
Honestly you can't trust the light on the board to completely diagnose all board troubles. I still suspect a stuck or sticking relay on the board.
 
  #10  
Old 07-25-06, 04:00 PM
Member
Thread Starter
Join Date: Nov 2005
Posts: 94
Received 0 Votes on 0 Posts
Originally Posted by Grady
Unless your thermostat requires a common for some reason (such as a light), having only a wire to the outdoor unit from "c" is completely normal.
Honestly you can't trust the light on the board to completely diagnose all board troubles. I still suspect a stuck or sticking relay on the board.
A stuck or sticking relay on the board......still means I need to purchase a new board....correct?? (I have a reset switch on my board...which I have pressed (5 sec) to no avail).

Regarding buying a board.....how does it typically work....if my furnace is still under warranty?

Do I get billed?....or does the Armstrong retailer simply bill Armstrong and send me along my board?

Thanks again.
 
  #11  
Old 07-25-06, 05:10 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 13,936
Received 1 Vote on 1 Post
Warranty

If the board is still under warranty, the distributor will provide the dealer with a new board at no charge. The dealer will in turn install the board & charge you only labor unless you have a parts & labor warranty.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: