Heater Control Board Wiring

No C stat and heater control board has X, R, B/C, G, W. Good with adapter for R, G and W, but not sure about Y. I’m assuming thru process of elimination, that Y = B/C. But then do I connect both the Y and C wires back up to B/C on board?

B/C is likely to be common with the number of wires coming off of it. I have a feeling that your Y wire does not go to your furnace, and instead goes directly to your outdoor unit. Can you share a picture of your existing thermostat wiring?

What is the brand and model of this air handler/furnace?

Thank you for reply! Attaching thermostat pic (RH, W, Y, G, unused black). Reading a bit more on the community yesterday made me realize that my A/C may be involved. I’ll have to check when I get home, but I believe heater is a Lennox from mid 1980s and is in attic. A/C unit I replaced about a year ago and put on roof. Other posts I read said G becomes C when using adapter. I’m starting to go cross eyed with all these codes, terminals and wires.

Looks like you can use that unused black wire for C and not use the adapter

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Well, I see 2 black wires attached to B/C on the furnace, If you’re lucky, one of the black wires goes to the thermostat, and the other black wire goes to the A/C unit. That will mean that you can just connect the wyze without modifying any wiring anywhere else, as follows:

old thermostat                                                 new wyze
Rh (orange wire)                       >                          Rc
W (white wire)                         >                          W1
Y (yellow wire)                        >                          Y1
G (green wire)                         >                           G
Not connected (black wire)             >                           C

Brilliant, so glad I checked on this community. Much appreciate your time and free advice. Not home at the moment, but will give this a go as soon as get there. Color me pleased.

Hmmm, would not power up. I’m afraid I gave up and put the old thermostat back up. I guess I need to do more research or swallow my pride and call a professional.

Do you have a multimeter? it would be helpful to check between the terminals on that furnace to make sure that there is at least 25VAC between R and B/C

Ah, the multimeter, the bane of my existence. Mostly because other than simple tasks, it baffles me. I have a very nice digital unit supplied to me by a cousin, but no matter how many YouTube videos I watch, I still can’t quite figure it out. I climbed into the attic again this morning (more times up there this weekend, than the last 20 years) and using the AC setting, set leads on the R and B/C like you suggested. I received 4 different readings, none of which were close the 25V. Obviously I am doing something wrong and quite possibly in over my head. Appreciate any further guidance, but would not blame you if you threw up your hands and/or rolled your eyes.

check the voltages between R and the other terminals. do any of them have 25V?
Whichever one has between 25 and 30V should be C.