I have a two zone heat/AC system with two air handlers and a single oil fired boiler. I’m trying to install a Wyze thermostat but there is no control board in the air handler. I have four wires (red, green, yellow, white) coming from the existing thermostat and there are two extra unused wires (brown and blue). I need to either use the C wire adapter or use one of the unused wires from the thermostat as a C wire. My issue is that I’m not sure where to connect the C wire on the air handler. Attached is a wiring diagram from inside the air handler. Any suggestions on where I could connect the C wire? In some of the other posts I’ve seen suggestions to get it from the transformer. Would that be the brown wire on the 24V side of the transformer as shown in the diagram? Thanks for any help or suggestions.
I have no idea, but it is interesting that the brown eventually runs into a c before the y
Yeah, I also thought that was a bit weird. Based on my other reading on this topic i thought y was for cooling.
it looks like Y goes to C after it goes though the cooling unit relay to turn on you a/c when Y is supplied power.
I think you could use an extra wire to go C terminal to C on the thermostat and hook the others up as usual.
Yes, the brown wire is the common wire.
If you have an extra wire on your run to the thermostat, i strongly recommend you use that and not the adapter, as it looks like your Y wire doesn’t go back to the furnace board directly.
Thanks, really appreciate your reply. Yes, I do have an extra wire going back to the thermostat and would definitely prefer to use that as well. So I would just splice onto the brown wire where I can, correct?
Yes. A common place to do it is the wire nut that feeds the compressor (Marked C on your diagram). For the sanity of the next person to work on your system, I recommend you use the blue wire in the thermostat wiring for the C wire.