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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 797
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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My fan won't stop running

Customer Question

My fan won't stop running
Submitted: 1 year ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 1 year ago.
Hi, I'm Brian and I'm here to help!
On a furnace, the most likely cause for this is the high temperature limit has tripped/failed or the roll out switch has tripped. It could also be a furnace control board fan relay failure. Both of these faults would continue to run the fan without the thermostat hooked up. The roll out switch is manual reset and it would even last through a power recycle of the furnace.
If you have a volt/ohm meter I can help you diagnose this problem.
Customer: replied 1 year ago.
I have a volt/ohm meter. What should I do?
Expert:  Brian HVAC Guy replied 1 year ago.
Very good then. Just so I make sure I get the right wiring diagram, could you please remove the blower panel of the furnace and give me the actual model number on the data sticker inside?
Thanks, -Brian
Customer: replied 1 year ago.
GUK100D20-1B
There is also a Trane heat pump. That can make the fan run also right?
Customer: replied 1 year ago.
Trane 4twx5
Expert:  Brian HVAC Guy replied 1 year ago.
Thanks for those numbers. Your thermostat is the only other component that will make your indoor fan run (beside the furnace control board). I will see what I can find for a wiring diagram and come back with some tests for you.
There is one test you can do now just to confirm 100% we don't have a thermostat issue. Remove the furnace blower panel, locate the low voltage wiring terminal strip where your thermostat wires connect. Remove the Red thermostat wire from the R terminal and wrap it around a wire so it won't contact anything. Put the panel back on the furnace and turn the power back on and tell me if the blower continues to run.
Try that and we will go from there. Meanwhile I will try to locate your furnace wiring diagram.
Thanks, -Brian
Customer: replied 1 year ago.
not seeing much that looks like a low voltage terminal strip
Customer: replied 1 year ago.
Did you get those pictures?
Expert:  Brian HVAC Guy replied 1 year ago.
Yes thanks for those!
Customer: replied 1 year ago.
I can pull the thermostat off the plate on the wall and the fan does not stop running.
Expert:  Brian HVAC Guy replied 1 year ago.
I understood about pulling the thermostat off but this test double checks that you have no shorts in the thermostat wire. It is just a double check to be sure. I want to make sure we're thorough and don't miss anything in the diagnosis.
Ok you are correct, you have no low voltage terminal strip. Your low voltage wires all connect in that group of orange and blue wire nuts on the right side of the furnace. If you can unwire the red wires, you can put the wire nut over the thicker factory wire and just make sure the other two red wires are disconnected and out of the way. That would be the same as the test I asked for above. Then power up and see if the fan continues. Thanks and sorry for the misdirection.
I am having some trouble locating the wiring diagram for your unit. Could you possibly take a nice picture of the wiring diagram as close up and in the highest resolution you can please? That will speed up this process a bunch!
Thanks, -Brian
Customer: replied 1 year ago.
ok
Customer: replied 1 year ago.
Wiring diagram
Customer: replied 1 year ago.
There were 3 red wires connected only to each other and 1 red and 1 pink twisted together
Customer: replied 1 year ago.
All disconnected
Customer: replied 1 year ago.
Nothing running now. No fan. Thermostat blank.
Expert:  Brian HVAC Guy replied 1 year ago.
Thank you for the wiring diagram pic!
Yes, I zoomed in tight on the one picture you sent after finding your control board online. It actually does have a low voltage terminal wiring strip it is just hidden behind that group of wires that are zip tied together. So short lengths of thermostat wire go to the terminal strip and then to the group of wire nuts. Sorry again for the misdirection.
So you disconnected the red wires and powered up and the fan stopped? But yet you took the thermostat off the wall and the blower remained running. All correct, yes?
Also, is this the first time you have powered the furnace down and back up? If you've powered the furnace down before, when you turned the power back on, did you still have the same problem with the fan running non-stop?
Customer: replied 1 year ago.
Yes.Yes, I have powered on and off before, both at the breaker and at the light switch on the side of the furnace. The fan always started right up,
Customer: replied 1 year ago.
Are you saying the lv terminal strip is the one on the right edge of the circuit board?
Customer: replied 1 year ago.
Ok. I put the wire nuts back on and disconnected the red wire from that terminal. Same thing. No fan running. Thermostat blank
Customer: replied 1 year ago.
Do I need to try to connect the red wire and take the thermostat off again??
Expert:  Brian HVAC Guy replied 1 year ago.
I'm sorry for repeating myself but the test you just performed points to a shorted thermostat wire and that is pretty rare so I just want to make sure.
Wire the red wires back together, pull the thermostat off of its base and power the furnace back up and let's triple check that the fan runs when it shouldn't be.
I fully expected this to be a problem with one of your heat cycle limit switches but like I said above, it's now pointing toward a thermostat wire issue between the thermostat and the furnace or possibly right there at the furnace. So, you should also take a really close look at all the small field installed thermostat wires for any abrasions or insulation damage. Both at the thermostat and at the furnace and where the wires enter the furnace through the cabinet. Especially the red and green wires. The red is 24 volt power and the green wire is the circuit that brings the fan on in cooling or fan ON modes.
Let me know what happens...
Thanks, -Brian
[edit] [read your last post while typing the response above. Yes, that's the low voltage terminal strip on the right edge of the board.] We may need to do more testing by removing some wires there, but for now just try what I have above first]
Customer: replied 1 year ago.
I hooked everything back up. Fan running
Customer: replied 1 year ago.
Took the thermostat off and it's not running now. Don't know how I screwed that up before
Customer: replied 1 year ago.
This thermostat
Customer: replied 1 year ago.
But only 3 wires. Does it communicate wirelessly to my heat pump controller?
Expert:  Brian HVAC Guy replied 1 year ago.
This looks like a Honeywell IAQ system. There should be what's called an EIM control board that those 3 wires from the thermostat run to. They normally are in a shallow white or greenish/tanish plastic enclosure that opens. This is kind of a game changer. We may have to shift gears a bit to trouble shoot this. See if you can find that controller board. It should be remotely installed from the thermostat area and usually they are installed close to the furnace. Take pictures of it please. Make sure the pictures show all wiring and cables. In other words, one close up and one a bit further back to show the cables.
Thanks, -Brian
Customer: replied 1 year ago.
You mean this box?
Customer: replied 1 year ago.
Open
Customer: replied 1 year ago.
Wiring
Expert:  Brian HVAC Guy replied 1 year ago.
Yep! That's the guy all right! That looks like an older Honeywell Comfort Control Center or a really early Honeywell Prestige IAQ system. Either way I can get the docs for it if need be. That controller has some functions in it to run the fan at odd times. It may be in system setup to run the fan occasionally. It could also be that the thermostat/EIM took a surge and got confused. The programming actually resides in the thermostat. Having it removed from the wall for a long period may have corrected your issue. It's hard to say. It appears to me this is a new problem so obviously it's not something you programmed it to do. I would put everything back together and see what happens. If the fan runs when you don't have the fan switch on the thermostat ON or the cooling or heating called for, we may have to go through the ISU table (installer set up table) in the thermostat and check the ventilation settings. Maybe something errantly got changed by a power blip. It's hard to tell.
Anyway, button everything back up and tell me if the fan still runs when it shouldn't be. We'll go from there. I do not think there is a problem in your furnace at all. It's not very likely it's a shorted wire either but you should definitely look over all the wiring as I suggested above for damage due to vibration.
We'll go from here...
Thanks, -Brian
Customer: replied 1 year ago.
All back together. Fan running again
Expert:  Brian HVAC Guy replied 1 year ago.
Ok, we have to figure out if it's the wiring, the board, or the thermostat telling the board to power the fan up.
On the back of the thermostat can you find the full model number of it please. It should be a TH94xxx-xxxx or something very similar. I need the exact number so I make sure I get the correct supporting docs for it and we get the right ISU table for it.
Also, at the EIM board remove the green wire on the right side of the board connected to G and tell me if the fan stops. You can do this with the furnace powered up. It's just 24 volts ac, it won't hurt you and it won't hurt the system as long as the green wire doesn't contact anything while it's disconnected. Let me know if the fan stops as soon as you remove the green wire. I'm 90% sure it will.
Customer: replied 1 year ago.
When I pull the thermostat off while its running it stays running. That must be what I did before
Customer: replied 1 year ago.
Th9421c1004
Expert:  Brian HVAC Guy replied 1 year ago.
Thanks for the model number, Yeah it would stay running, that confused us both. At the time I didn't realize you had an EIM attached. it just stays in the mode it's in when you pull the stat. It definitely led us astray for awhile.
Customer: replied 1 year ago.
Yes. It stopped when I pulled the green wire
Customer: replied 1 year ago.
should i hook the green wire up again?
Expert:  Brian HVAC Guy replied 1 year ago.
Ok, at least now we know it's not in the wiring. It could also be that one of those off white relays on the board has stuck closed and is the system is not actually calling for the fan to run. Wire the green wire back up and try knocking lightly with the handle end of a screwdriver on the white relays. Tap, Tap, Tap... not too hard but hard enough to unstick the relay if the contacts are stuck. Meanwhile I'll pull the manual for the thermostat and we'll go through the ISU and see if a setting got messed up.
Customer: replied 1 year ago.
No luck tapping
Expert:  Brian HVAC Guy replied 1 year ago.
It was a longshot but sometimes it works and tells us the relay is shot.
I'm still looking for the correct docs. I was right, it's the older Total Comfort Control IAQ by Honeywell. It is one of the first types of this system they sold. I'll be back soon, I have a bit of studying to do. Thanks for your patience...
-Brian
Customer: replied 1 year ago.
Ok
Customer: replied 1 year ago.
hows it going Brian?
Expert:  Brian HVAC Guy replied 1 year ago.
Ok I finally found the right doc and the right ISU. Phew!!...
We are going to have to enter installer set up and see if that's the problem. First let's see what your ventilation settings are. With everything powered up, at the thermostat press the more button until the ventilation setting are displayed. It should page from Humidification to Dehumidification and then to Ventilation. The screen should show two sets of up and down arrow keys with VENT xxx Minutes in between the sets of arrow keys and Auto or OFF on the left of them. Tell me what those settings are and we'll go from there.
Customer: replied 1 year ago.
4 screens in sequence when I hit more
Customer: replied 1 year ago.
None exactly like you are describing
Customer: replied 1 year ago.
do you mean the first one in the sequence of pictures I sent??
Expert:  Brian HVAC Guy replied 1 year ago.
And that's it? No more screens other than those if you continue to press more?
Customer: replied 1 year ago.
nope. just cycles through those 4
Customer: replied 1 year ago.
it doesn't matter if it's in cool, heat, off or emergency heat - just cycles through those 4 screens
Customer: replied 1 year ago.
still there Brian?
Expert:  Brian HVAC Guy replied 1 year ago.
Ok it doesn't appear your original installer set the ventilation up for you.
Now we're going to have to get into the actual ISU to check some things...
Ok to enter Installer Set Up, press the system key once. Now press and hold the two blank keys on either side of the center key on the bottom row until the screen changes.
You should see a screen with a small 4 digit number on the left with a set of up/down arrow keys to the right of it, followed by a bit larger 2 digit number finally followed by another set of up/down arrow keys on the far right. The smaller 4 digit number it the function number and the larger 2 digit number is ***** function's parameter.
We are gonna scroll down to function 400 Ventilation using the up/down arrows next to the function number. Tell me what that function's parameter is please.
Thanks, -Brian
Customer: replied 1 year ago.
400 on left
0 on right
Customer: replied 1 year ago.
that sound ok??
Expert:  Brian HVAC Guy replied 1 year ago.
Ok so it's not the ventilation setting causing this. That setting at 0 disables ventilation control. I kinda figured that since ventilation didn't show up in the more screens but we had to check to be sure.
Now we are going to the end of the installer set up until you see test kind of awkwardly spelled where the function number would be. So scroll up in function number until you see test. There should appear a large single digit number above the left arrow keys. Use the left set of arrow keys to change that number to 2. Now use the right set of arrow keys and toggle slowly between 0 and 1. 0 = Fan Off, 1 = Fan ON. I'm not sure if your Armstrong furnace has an off delay on the fan when the fan output is turned off. You may have to wait a bit. If the fan turned off immediately way earlier when you removed the green wire from G then there is no off delay. The fan should turn on and off as you toggle the test parameter between 1 and 0 respectively.
Let me know how that test goes....
Expert:  Brian HVAC Guy replied 1 year ago.
I'm sorry, I'm getting tired...
Use the right set of arrow keys to toggle between 0 and 1 is what I should have said!
Customer: replied 1 year ago.
yes that works
Customer: replied 1 year ago.
fan turns off when I go to isu mode
i go to test and change left arrow to 2 then right arrow controls fan
Customer: replied 1 year ago.
0=off 1=on
Expert:  Brian HVAC Guy replied 1 year ago.
So you can turn the fan on and off with that test function and the fan actually turns on and off as it should?
Customer: replied 1 year ago.
yes
Expert:  Brian HVAC Guy replied 1 year ago.
Um...ok...
Exit the installer set up by pressing the DONE key on the far lower left.
What is the position of your Fan function mode (above the system mode column) from the home screen. Auto or ON? (I assumed you had the fan function in Auto but I didn't actually ask earlier!) I'll be really ashamed of myself if that's the issue!
Customer: replied 1 year ago.
auto
Expert:  Brian HVAC Guy replied 1 year ago.
And yet the fan is still running non-stop even if the system mode is set to off?
Customer: replied 1 year ago.
Tes
Customer: replied 1 year ago.
Yes
Customer: replied 1 year ago.
Stops when I go into isu mode
Customer: replied 1 year ago.
Starts again when I go out of it
Expert:  Brian HVAC Guy replied 1 year ago.
Wow that is really bizarre! Give me a moment to look through the entire ISU for something else that could possibly be keeping your fan on. I thought I covered everything, all the tests checked out ok, I'm a bit stumped!.... Thanks for your patience!
Expert:  Brian HVAC Guy replied 1 year ago.
Could you please get back into ISU mode and tell me the parameter settings of ISU 370, 372 and 374? and then ISU 379, 384 and 391 please? Note that some ISU numbers may not appear depending on a previous ISU number so just note that it doesn't show up.
These are the only other ISU's that can affect the fan mode.
Customer: replied 1 year ago.
370 1
372 3
374 0
379 0
there is not 384 or 391
Expert:  Brian HVAC Guy replied 1 year ago.
Try setting ISU 370 to 0 and see if the fan behaves normally then please.
Thanks, -Brian
Customer: replied 1 year ago.
fan still on
Customer: replied 1 year ago.
Why would one of these settings be wrong? I never changed any
Customer: replied 1 year ago.
should i set 370 back to 1?
Customer: replied 1 year ago.
brian if you are still there i need to go to sleep soon
Customer: replied 1 year ago.
please leave me any more instructions or anything else to try
Expert:  Brian HVAC Guy replied 1 year ago.
Your thermostat system is basically a small computer. It is subject to the same things a computer or building automation system is. I was a building automation contractor in Florida for many years and I saw times where the awful power we had there and terrible lightning could scramble the memory map in a control from a surge or droop. It's odd but it does happen. We've covered the hardware part of the system with the wiring and the relay testing so all that's left is the software.
I'm afraid I'm at the end of ideas at this end. We can try a system reset as a last attempt, unfortunately that will wipe any user programmed options you have including scheduling, frost protection and setpoints.
Yes, you should set 370 back to 1. However, performing a full system reset may take away those settings. It would appear the only one you have is humidity control and frost protection though so not too bad. Unfortunately any scheduling will revert back to default and I believe even the system settings will revert to default so there would be some reprogramming to do for sure!
Let me know how you want to proceed? And yeah, I need to log off as well. I have a trip early in the morning. The only thing we have left to try is system reset. Perhaps we can get a fresh start tomorrow afternoon?
Thanks, -Brian
Customer: replied 1 year ago.
Please tell me how to reset and reprogram. I will wait til you are back on line to start the procedure.
Expert:  Brian HVAC Guy replied 1 year ago.
Good afternoon! I'm sorry it took so long to get back to you. The morning trip took longer than I anticipated.
The reset for your Honeywell control system is in the installer set up. It's ISU number 710. You simply change that function's parameter to 1 then back to 0. I don't remember if it gives you a warning and a chance to cancel. I've only done this once on the IAQ/EIM type system and don't remember. After performing that reset you should also remove the battery in the thermostat and power down your furnace to remove ALL power to the control system for 5 minutes or so. Just to doubly ensure your system is reset from scratch!
After that, replace the battery, power up the furnace and you will have to proceed with programming the system through the ISU table. I would turn power off to the OUTDOOR unit during the reprogramming. It's not necessary for that unit to be powered up during all this. Below are links to both the ISU table and the operating manual for your thermostat. You will find the pdf with the ISU table is quite extensive. Fortunately it is also very thorough and gives an explanation for all ISU's. The important settings are in the beginning of the ISU, set the date and time, the system type, the number of stages of heating and cooling. The fact that you have a dual fuel heat pump system will affect MANY ISU's! I can help with that if you have questions.
ISU programming manual:
http://site.theenergyconscious.com/pdf/pow-honeywell-0009-Product-Data-Home-Comfort-System.pdf
Thermostat operating manual:
https://customer.honeywell.com/resources/Techlit/TechLitDocuments/69-0000s/69-1815EFS.pdf
If you'd like, I can offer an Additional Services offer where I will create a document giving you ALL settings for your ISU table. I can do that for an additional $50. To do that I would need some additional info from you, such as your zip code for average weather conditions in winter, what kind of humidifier you have and likely others that I can't think of in the moment.
Bear in mind this is kind of a last ditch effort. Your system is confused with the fan control and I can't guarantee that it will recover properly. We may do all this and end up in the same boat. Whether it's worth it, is up to you!
Let me know how you want to proceed and I'll help in every way I can.
Expert:  Brian HVAC Guy replied 1 year ago.
I just had another thought. There is a way around this but it's not without its sacrifices.
If you never use your furnace fan in the ON position, meaning you just allow the call for heating and cooling to run your fan and never put the thermostat in the Fan ON position, you can wire it to do that and solve your problem. It wouldn't really affect your control system unless you have it set to humidify without the heat being on.
Let me know if you're interested in that approach.
Thanks, -Brian
Customer: replied 1 year ago.
are you sure this would work? How do I do that? What would happen when I put the fan in ON mode after the wiring change?
Customer: replied 1 year ago.
Hi Brian, are you there????
Customer: replied 1 year ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from yo. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 1 year ago.
Can you tell me how to do the wiring change??? I think I should try that next. Thanks
Expert:  Brian HVAC Guy replied 1 year ago.
Sorry for the slow response. I had to step away for a bit. I should have logged out but left quickly and left my laptop open.
Ok if you make the low voltage wiring change all you have to do is, at the EIM control board, on the right hand side, the green wire you removed earlier, the one that brings the furnace fan on, move that wire up and connect it along with the yellow wire in the Y connection.
What this does is send a signal to bring the fan on whenever the compressor is called for. If you are in emergency heat, the circuitry withing the furnace will bring the fan on itself.
The only problem with this is you lose independent fan control. When you put the thermostat fan switch in the ON position, nothing will happen and nothing will change since the fan on position energizes the relay at the G terminal where you removed the green wire. Since there is nothing there, nothing will happen.
This is a common procedure and is done a lot in other installations where an extra wire is needed because in those cases the Y terminal is jumped to the G terminal at the furnace then it frees up the green wire. Of course that's not what you're doing. You're doing it because your fan runs errantly when it shouldn't be.
The wiring change is a very last ditch effort and you should resort to that only if resetting the system doesn't work. I think it's worth the time and effort to try the reset first then if that doesn't work, do the wiring change. It saves you from having to scrap the control system for a new one.
Bear in mind if you do the wiring change that the thermostat will not have independent control over the fan. So any control scheme in the ISU that is dependent on running the fan will not be able to be used. The only one I can see that you MAY have used is to humidify your home even when the heat wasn't on. You will lose that capability but you can still use the Humidify only when heating feature in the ISU to humidify your home. That is set in ISU 374 and was already set to only humidify in heating anyway. You really won't lose anything except being able to turn the furnace fan on by itself for circulation only. Most customers don't do that anyway.
Let me know how you want to proceed. I will present the offer to give you ALL the ISU settings in a pdf file. You can choose whether or not you want to accept it. We can still continue our conversation here if you don't accept it. You are still welcome to ask my opinion on what a particular ISU should be set at even if you don't accept. The offer, if accepted, simply gives you ALL the recommended settings for your particular system in a pdf that you could even print so reprogramming after the reset becomes a no-brainer! It's all up to you though.
Thanks, ***** ***** again for the wait.
Customer: replied 1 year ago.
I will try the wiring change first. Thanks
Expert:  Brian HVAC Guy replied 1 year ago.
Ok very good, let me know how that goes. I'm sure it will work fine but you should cycle the thermostat through all the heating and cooling modes, including emergency heat, to be sure the fan comes on at all times when it's supposed to.
Thanks, -Brian
Customer: replied 1 year ago.
will fan mode circ still work??? or only auto
Expert:  Brian HVAC Guy replied 1 year ago.
No, the auto circulation feature won't work either, no matter whether timed or random. The fan switch will have absolutely no control over anything in any of its positions (settings). The ONLY time the furnace fan will run is on a call for cooling or heating, period.
Thanks, -Brian
Customer: replied 1 year ago.
I think it works now in all the modes. Thanks much. I will think about doing the reset and let you know. Lots of codes to reset. Would you be able to know what all the codes need to be without seeing the furnace or heat pump?
Expert:  Brian HVAC Guy replied 1 year ago.
That's good that the fan works in all modes. That is a quick and dirty fix but effective for the most part. You're very welcome.
Yes, I enough information already to give you the correct codes for your system without needing anything further except your zip code. The table format I do this in (I have done this for quite a few customers here) is:
ISU# Function Type Function parameter Additional details or options
This way any ISU's that are optional and a decision for you, I note them. It's like the one in the book only for YOUR system instead of everyone's system. The only additional thing that would be helpful is your zip code so I can look up typical and average winter weather conditions for your area to recommend the dual fuel switchover values and window protection settings. I have all the rest of the info I need.
I'm glad we got the fan to behave better. All you have to do in the future is accept the additional offer if you choose and I would begin work on the table.
For now, if we're finished with your original question, a positive rating would be appreciated(bonuses are always greatly appreciated!) You can still accept the offer after rating and still post follow up questions that relate to the original question right here on this question by just replying. That is no additional charge. Thanks for allowing me to help you with this challenging issue and thanks for using Just Answer!
-Brian
Thanks, Brian
Customer: replied 1 year ago.
with all the codes I imagine the restart is about 15 or 20 minutes? is that right?Also, if that did not work I would need to get a new thermostat???? Or could it be anything else?
Customer: replied 1 year ago.
or just a new eim?
Expert:  Brian HVAC Guy replied 1 year ago.
It shouldn't take you long to enter the codes if you're just entering them from a list. I would think 15 or 20 ought to do it. It could take hours and lots of reading, head scratching and hair pulling to read the manual and program it! I know my first one did! The newer Honeywell systems like this have a micro sd card to make it lightning fast once a standard ISU set is created. There is a backup and restore function in them. Unfortunately that is a function within the thermostat not the EIM. They have come a long way though!
It's hard to say whether it's the EIM or thermostat doing this. It could be either. I've never had one of these systems with this particular problem. The EIM is definitely cheaper! If the reset doesn't work I would definitely try replacing the EIM first!