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Webb-Guy
Webb-Guy, HVAC Mechanic
Category: HVAC
Satisfied Customers: 1443
Experience:  maitenance tech at casto
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I replaced my thermostat and now the furnace blower won't

Customer Question

I replaced my thermostat and now the furnace blower won't turn on. It is giving an error of "reverse polarity, poor ground". (The thermostat is the same as what I replaced, so the wiring went in the same way.) What do I need to fix?
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: I am not sure. Everything was working fine with the blower, the a/c, etc. before the replacement. I replaced the thermostat because the digital display and buttons were not working. After the replacement the furnace blower would not come back on and that error signal was flashing. The a/c outdoor unit is working.
JA: Do you plan on doing the work yourself?
Customer: If it is a simple fix, yes.
JA: Anything else we should know to help you best?
Customer: Not that I can think of.
Submitted: 6 months ago.
Category: HVAC
Expert:  Webb-Guy replied 6 months ago.

So since the outdoor unit is working its a possibility that wires are touching inside the thermostat. Since you just changed it that is something you will need to check.

Expert:  Webb-Guy replied 6 months ago.

If you have found this information helpful and it solves your problem all I ask is you rate with 5 stars at the top so I am credited for my time. Rating does not stop you from getting back to me in the event you need me.

Customer: replied 6 months ago.
I have double checked the wiring and nothing is touching or loose. Is there anything else that would cause the "reverse polarity, poor ground" error at the furnace?
Expert:  Webb-Guy replied 6 months ago.

Try swapping the low voltage wires on the board. They are usually marked s1 and s2 and come from the low voltage side of the transformer on your furnace.

Customer: replied 6 months ago.
Just to be certain, what other label might they have? I do not have anything identified as s1 and s2.
Expert:  Webb-Guy replied 6 months ago.

You have three wires coming to your house from the utility. Two are "hot" wires and the third is a neutral wire. The voltage between the two hot wires is 220-240 VAC. The voltage between a hot and neutral wire is 110-120 VAC.

You furnace is presumably designed to operate on 120 VAC, which requires a connection to the neutral line and a hot line. (There's also presumably a green ground wire).

These neutral wire is designed to be connected to a specific connection on the furnace, and so is the hot wire. Thus they are "polarized." If the wires are connected in reverse, you get the polarity error code.

Other things can cause that as well, such as a defective circuit board.

Customer: replied 6 months ago.
Ok, you are confusing me with your latest response, because I did not do anything to the wiring at the furnace. Is there a way these wires would become reversed if I did not change them (the unit was working properly before the thermostat change)? Go back to s1 and s2: are there other labels for these wires?
Expert:  Webb-Guy replied 6 months ago.

Sorry I did not mean to send that message if you did not change your wires on the furnace at all either something is not right with the furnace wiring and that is why it is giving you this error or something else is going on

If you are not seeing the s1 and s2 terminals in your thermostat it doesnt apply to yours. What thermostat do you have?

Customer: replied 6 months ago.
Furnace is a Trane and thermostat is a White Rodgers programmable.
Customer: replied 6 months ago.
I see s1 in the thermostat, s2 maybe where I can't see it, but there are no wires that I can manipulate associated with it. What color are these wires typically on the furnace board?
Expert:  Webb-Guy replied 6 months ago.

Which white rodgers thermostat do you have?

Customer: replied 6 months ago.
1F80-361
Expert:  Webb-Guy replied 6 months ago.

Do you know if you have the 5 wire two transformer system set up?

Expert:  Webb-Guy replied 6 months ago.

Trying to figure out which wiring set up is for yours?

Expert:  Webb-Guy replied 6 months ago.

http://s3.supplyhouse.com/product_files/White%20Rodgers%20-%201F80-361%20-%20Configuration%20Guide.pdf

You may have better luck looking at it yourself since the unit is in front of you.

Expert:  Webb-Guy replied 6 months ago.

We currently have a storm coming in if I loose internet I will be sure to message you once its back up. Just in case so you dont think I left you

Customer: replied 6 months ago.
checking it out...it seems to be the 5 wire, 2 transformer set up
Expert:  Webb-Guy replied 6 months ago.
Ok have you checked to make sure all your wires are the same as the wiring diagram for that?
Customer: replied 6 months ago.
I believe the wiring is correct. Here is a photo. I will send a couple more of the wiring at the thermostat and furnace. I did not change anything with the furnace. Turned off power to the furnace and air conditioner at the fuse box, swapped out the thermostats, turned power back on and then no-go at the furnace.
Expert:  Webb-Guy replied 6 months ago.

Is your furnace electric or gas?

Customer: replied 6 months ago.
Gas
Expert:  Webb-Guy replied 6 months ago.

Did you turn off the breaker when you changed the thermostat to the furnace?

Customer: replied 6 months ago.
for the furnace and the a/c unit.
Expert:  Webb-Guy replied 6 months ago.

Your unit looks wired correctly. The only other possible that maybe the fuses in your furnace blew on the board when you changed to the new thermostat. Can you gain access to the board?

Customer: replied 6 months ago.
Do you mean a fuse on the board I photographed? Or is there another fuse to look for?
Expert:  Webb-Guy replied 6 months ago.

yes on furnace one picture you will see a little brown fuse off to the left on the board with a number 5 on it.

Customer: replied 6 months ago.
I don't know how to tell if the fuse is bad. May need to get a replacement to try out.
Expert:  Webb-Guy replied 6 months ago.

That would be best. Fuses are not expensive and easy to replace. Let me know how it goes. I certainly hope this helps fix your problem. I know this has got to be frustrating for you. In the event it works all I ask is you rate with 5 stars at the top so I am credited for my time.

Customer: replied 6 months ago.
I certainly will. Thank you.
Expert:  Webb-Guy replied 6 months ago.

You are very welcome.

Customer: replied 6 months ago.
Unfortunately a new fuse did not do the trick. Any other thoughts?
Expert:  Webb-Guy replied 6 months ago.
Why don't you try putting the old thermostat on It to see if that works. Maybe the problem is with the thermostat. That's the last thing I can think of
Customer: replied 6 months ago.
Tried that with no luck. I flushed my condensate line because I noticed some water dripping while I was working at the furnace. Would that in any way relate to the problem I am having?
Expert:  Webb-Guy replied 6 months ago.
Only in the event that you got the board or something wet while doing that. At this point I can't think of anything else because the only thing that will give a gas furnace reverse polarity is the fan motor has went out or the board. Since the board is telling the ac to come can only mean some how one way or another the motor went out on you. Did the furnace work before doing any of this. Did you turn it on and it was working before any of this?
Customer: replied 6 months ago.
The only problem at the beginning was that the thermostat display wasn't working right and it wasn't responding to the programming buttons to adjust temp. Blower motor was replaced last year.
Expert:  Webb-Guy replied 6 months ago.
It just doesn't make any sense unless there is a wire broke in the wall the thermostat is bad or the motor has went bad. There is not any other thing I can think of. You should not be having this much trouble
Expert:  Webb-Guy replied 6 months ago.

Have you figured anything else out??

Customer: replied 6 months ago.
No, not yet. Not sure what else to do beside calling in a professional to look at it. That will have to wait. I may try to work it through some more later tonight
Expert:  Webb-Guy replied 6 months ago.

Well I am certainly willing to continue assisting if you would like.

Customer: replied 6 months ago.
If anything comes to mind please let me know. I will touch back when I have a chance to get back to it tonight.
Expert:  Webb-Guy replied 6 months ago.

Sounds good.