Thermostat C-Wire Adapter question

Just bought a house and went to hook up our Wyze Thermostat and had some confusion, that I am hoping this forum can help me understand.

The house has 2 AC Units outside (And older looking one and a pretty new looking trane). There are 2 thermostats one upstairs in the Bonus room area and one downstairs.

The upstairs up is for the newer Trane AC Unit and has its own smart thermostat.

Went to hook up the one downstairs and it mentions I need the C-Wire Adapter.

Where I am confused is when I look in the area above our garage I see one Unit, a Trane is this normal that even though we have 2 units outside it is just one inside and would the control board be on that. Of note the power is also separate as I turned off the Heat and Power at the box in garage and the upstairs unit was still able to turn on while the bottom did not. Figure if so I will have to turn the power off to that also.


You probably have a crawl space or an attic that contains the other inside unit. Either that, or one of the outside units is a package unit, with ductwork going through the wall of the building. If you show your current thermostat connections, I can tell you if you really need the C adapter.

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My last house had the air handler in the attic for the upstairs unit. If the vents are coming out of the ceiling upstairs, that’s probably where it is.

I saw crawl space area upstairs but when looking in only saw duct work.

Current thermostat wiring

House does not appear to have crawl space under is on a slab.


Hmm, Don’t see an extra wire, but there could be one in the wall. Do you have a picture of the wire connections on the air handler?

That is where my confusion started, is that the one device I found in the crawl space above garage. It had a panel that looked to need screws to remove and had not done that as was not sure if was for which unit. From some google searches it sounds like its possible to have 1 air handler (I figure device above garage) with 2 units outside.


It’s possible, but pretty uncommon. Usually if that’s the case, one of the outdoor units is no longer hooked up. There’s usually only 1 coil on an inside unit, adding another in series introduces a lot of air resistance.