Looking to hookup a wifi (smart) thermostat that requires common constant low voltage power. The hookup of the old thermostat didn't use the blue wire as it was shoved into the wall but I traced it up to the air handler.
Below is the electrical diagram as well as an image of what I've already done.
The blue wire wasn't connected to anything in the air handler. I used the wire nut that was there already being used for a thick and thin blue. That is what I did to my other one in the house and it worked. This one did not.
I've written some notes on my 2nd picture circling the "c" wire that goes to the thermostat, how I plugged it into the wire nut, and then showing a trace of that thick blue wire and where it goes with a zoom of where it goes. It mounts to the metal with a screw as a ground. This did not work as the thermostat didn't light up.
I believe that in my 2nd photo the ORANGE arrow is where I am really suppose to tap into (blue coming off of the circuit board). I don't want to do anything without a little bit more confidence though.
Any help or suggestions is much appreciated.
UPDATE: I've now updated wires. I'm only referring to BLUE wires, but I use overlay color to describe.
A - Green B - Pink C - Orange D - Turquoise