I have 2 wires coming up from my basement oil fired furnace and 3 wires coming from my central air handler in attic I am trying to hook up a Honeywell WiFi thermostat. The 2 wires from the basement I believe are easy to hook up. One goes to white and one to Rh. The three from central air are green yellow and red. Which I believe will go to green, yellow and Rc. The question is I have no blue wire, C wire. If I look at the terminal in the attic is shows a blue wire on one side but does not label it C. ( see attached pic). Can I run a wire from #5 to C on thermostat enter image description here

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1 Answer 1


You are correct

Based on the wiring diagram and provided photo, you appear to be correct that terminal 5 on your air handler's control block is your C terminal. So, go ahead and run your new thermostat cable, using that as C while matching the existing wiring for the remaining connections.

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