I am trying to install a new wifi stat. The wiring seems to all be there but apparently not connected correctly. So far I have tried using the green wire from the furnace, the blue and the white from the air handler, each as the C wire, all without luck (doesn't turn on when power is restored at breaker).
Behind the old stat, the upper cable goes to the air handler while the lower cable goes to the furnace. The white, brown, and blue wires in the upper cable were unused in the old stat while the lower cable's green wire was also unused.
In the air handler (a trane twe048c140c0), the brown and blue wires are unused. Do I need to connect either to one of the existing wire nuts?
I'm not sure why the furnace isn't providing 24V either, but possibly because the relay switch is bad? The furnace works fine otherwise.
Here is an image album displaying all wiring that leads to the stat from the air handler and furnace: https://imgur.com/a/uecMa
EDIT: Solved. There were two white wires hidden in the loops. None of the three spare wires running to the air handler were connected. Connected blue and stat powers on.