How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask BillyHvac Your Own Question
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22672
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Type Your HVAC Question Here...
BillyHvac is online now
A new question is answered every 9 seconds

I have a Payne forced air furnace model PG9YAB. I am

This answer was rated:

I have a Payne forced air furnace model PG9YAB. I am installing a new thermostat, which needs to have a wire connected to the C. On the furnace there is already a wire connected to C. In the thermostat area there is an unused black wire. Can I put 2 wires on the C terminal of the furnace?
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I had the previous thermostat installed professionally and when he was done there was one unused wire - a black one, which also seems to go to the basement furnace and is connected there to the Y terminal. The people from Honeywell didn't say anything about filters, so I don't know if you mean just the regular furnace filter. They said to ask Payne if 2 wires could go to C.
JA: Do you plan on doing the work yourself?
Customer: Yes.
JA: Anything else we should know to help you best?
Customer: Not that I know of. It's a wi-fi thermostat.

sorry for the you still need help?


Short answer is yes.....C or Common is like a neutral can heve multiple wires on C.

A thermostat, ac, humidifier...anything added that runs on 24v uses C as the common.....much like the negative post on a battery...

So multiple wires are normal on C terminal

Customer: replied 4 months ago.
Thank you. I can connect the unused black to the C in the thermostat area and then move the black that's in the basement to the C on the furnace. Right?

you are correct....spare black to C in other en d in furnace spare black to C

Customer: replied 4 months ago.
The thermostat still does not light. Should I call Honeywell tomorrow or do you have any ideas?

Did you have power off to the furnace? there a light lit on circuit board in furnace?

Customer: replied 4 months ago.
I will double check, but it should be on, because they said to turn it off while working. I did not see a light on the circuit board, but will look again. Thank you.

should be able to see the light through a small window in bottom door...or if door off make sure bottom door is on securely so that a pop out safety switch is fully depressed down

any luck?

Customer: replied 4 months ago.
much as that might be nice, then I might as well have scheduled a service call, which I may end up having to do anyway. There do not seem to be lights on the furnace panel and my thermostat is still not working.
I had trouble determining the color of the unused wire. This time it was clear to me that it was blue, not black (in the thermostat box). I connected that to the unused C terminal in the thermostat box area. Then I went in the basement and there was an unused blue wire that was wrapped around some wires that were in use. I unwrapped the blue wire, stripped the plastic off, and attached it to C. Honeywell says the C is the important terminal. Anyway, no go.

Did you see the pop out switch that protrudes when bottom panel is off?

Customer: replied 4 months ago.
Where is the pop out switch? How will I id it?

Ok......first the bottom door put back on the furnace securely and correct?

Customer: replied 4 months ago.
I left it off until I know things are working. It takes a while to get it off and on. Do you mean it won't work without the door in place?

Correct.....a button pops out cutting power to the unit as a safety device....the bottom door must be back on

Customer: replied 4 months ago.
thank you. I will go do that.

I will standby until I know you are all set

Customer: replied 4 months ago.
It still won't work, but the pop out is the dark brown or black triangular thing that goes back in place when you screw the door on. can tape it down for testing..

Customer: replied 4 months ago.
I don't know what else to do. The blue is connected to the C in the thermostat and the blue is attached to the C (along with a light yellow or cream one) on the furnace. According to Honeywell, if Payne said i could have more than one wire on C, I should do it and it would work.

can you take and post a pic of the circuit board wiring so I can see what wires you used? There may be more wires..

Customer: replied 4 months ago.
how do i post?

on your end you should see an attach files link..or a paper clip.

Customer: replied 4 months ago.
pic. sorry it's not very clear.

are you sure the blue at the the same blue wire as at the thermostat?

There are multiple cables and easy to confuse......we want to make sure it is the same wire end to end and not just another blue..

Customer: replied 4 months ago.
I just assumed they were the same because they were the same color. I will go look at the wires again.
Customer: replied 4 months ago.
here is a picture of the source of the wires on the furnace and a pic of the thermostat wires. The blues seem to be the same.

I think you have the wrong cable.....locate the G terminal on circuit board with green wire....follow that wire....then tell me if you see another blue wire in the cable the green goes to.

Customer: replied 4 months ago.
This house was built in 1958, and the wires that go to the furnace seem to come from 2 sources. One bundle comes from a dirty white wire and the 2 wires that come out of that are black and beige. The other bundle of wires, which I sent you a picture of, comes from a brown wire and the 5 wires that come from that are green red, yellow, whitish, and blue. There is not another source for either a blue or a green wire, and the blue wire is a bright blue like in children's first blue color they learn.

see here and tell me if the blue with arrows to it is the exact blue hooked to C

Click here

Customer: replied 4 months ago.
that's the one.

ok I was seeing this pic HERE and it appeared to be coming out of the other cable and one lokked dingy and used while the other appeared more "fresh.

do you see the blade yellow fuse near the G terminal?

Customer: replied 4 months ago.
since it wasn't being used, is it possible that it has somehow been disconnected, and I have to use the green one and then create that little arc thing with the copper wire?
Customer: replied 4 months ago.
I see the yellow thing, but I didn't know it was a fuse.

Just look at the side of it to see if the thin filament is still intact...the fuse pulls straight out of the board.

Then if it is not blown....

At thermostat move green to C (G will be empty at thermostat)

At furnace move green to C

Then make a short wire and attach one end in G and the other end in Y.

Customer: replied 4 months ago.
I couldn't see anything wrong with the yellow fuse. I pulled it out and then put it back in place.
Since the blue wire wasn't being used, when I do what you said above with the green wire, I then remove the blue wire and put it back where it was and disconnect it from the thermostat, right?
thank you for your help. At least I know the blue wire isn't going to work. If the green doesn't work, that let's me know, it's beyond my ability to make it work.
By the way, I like your dog.
I will wait long enough for you to tell me that I'm right about what to do with the blue wire at both ends.
Again, thank you.

Remove blue wire from thermostat

remove blue wire from furnace circuit board

Then do the green procedure as mentioned.

I wish you the best and hope all works out....

If the green does not work then you will need to call for service....fingers crossed!

When all set just "rate service" to move off the active list.


BillyHvac and 3 other HVAC Specialists are ready to help you
Customer: replied 4 months ago.
How long do I have access to your help for the fee I paid? If it's only tonight, I might was well rate you now.