enter image description here

I’m installing a new WiFi thermostat that needs the c wire. I ended up running new thermostat wires that contained the common wire but now I’m stuck on where to connect it to the furnace.

Can someone take a look at the wiring diagram to help me figure out if I have a place on my furnace to connect the c wire?

1 Answer 1


The AR861 doesn't provide that functionality, sorry!

Unfortunately, the AR861 does not provide a C wire from its internal transformer, so you'll have to use an external transformer on Rc and C with the supply from the AR861 connected to Rh on the thermostat.

  • You'll have to dig inside the furnace to find the transformer and its 24VAC wires. It's also possible the neutral side of the 24VAC is wired to the furnace's metal frame.
    – Stavr00
    Dec 6, 2017 at 18:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.