Trane TCONT802AS32DA wiring

I'm trying to decipher the wiring from my Trane 2TWZ9 heat pump, Trane 2TEE3F65A1000A air handler and Trane t-stat. one note on the pictures, the brown wire on the bundle at the outside compressor is spliced in the attic to another bundle with all matching except the brown becomes blue. In the air handler low voltage connection it looks as if the blue is just terminated there and never is wired to the t-stat as any color wire.
The t-stat never runs without the 3 AAA batteries. all of this information is because i want to replace the Trane TCONT802 with some smarter thermostat, like a idevice or T5+, one that is Apple Homekit enabled.

any help to decipher and help with a common to the t-stat bundle would be helpful. oh and in case you can't see it well the t-stat wire bundle is 18/6 and the "brown" wire is unused at both ends!
ps. added a closer maybe better angle on the air handler connections.

Thanks - Mark

 

Welcome to the forums.

Looks like no back up electric reheats...... is that correct ?

Air handler manual


R - red
O - white
Y - yellow
G - green
Y2 - blue
You will need an additional wire for C is using a wifi stat.

 

Correct. it's my understanding that it is (from my reading of the manuals, etc) an 2H/2C system. no electric heat.

 

Thank you Pete. In my scenario is there somewhere that i can pull the common? The t-stat wire bundle has an unused wire, but I'm not sure to what terminal not the LVTB I would wire it to? the existing B? That would complete a circuit from the thermostat to the air handler and then to the outdoor compressor unit. I just wasn't sure about that, as I did the worst possible thing last Sunday and tried to wire the spare wire to the LVTB blue terminal and then to the B screw down on the thermostat. Somewhere along the way I shorted out the 240V/24V transformer as I was screwing down the wire (YES i was lazy and didn't throw the breakers!!) and so spent $$$ to have my PMA vendor come out and diagnose and replace it for me. With a better one (70ka and a build in CB) but still!

 

On a Trane..... the low voltage B terminal is the common or C connection. That blue wire currently on the B terminal goes to the outside condenser. Even with a 70va transformer with a circuit breaker...... I'd recommend a fuse in the transformer line. I usually use ATC-4 fuses and fuse holders.

 

Thank you again. And to correct myself, I said in original post that brown wire from condenser was paired with blue, but you were gracious enough to not point out that I messed up! which i just realized I did as it is paired at the splice with a GREEN wire that is then terminated at the Y terminal at the LVTB. All the color mixes drives me crazy and I imagine any tech that I would call to do the same thing!
I just could not figure out why the installers never connected a common to the stat B terminal to power the stat all the time.
Regardless, your help is truly appreciated and i'll look to put in a fuse on the transformer blue termination on the LVTB reverse side when I install the new stat!

 

Update-received my ATC fuse holder and fuses (via A-i'm just lazy!) and spliced in-line on the blue 240VAC/24VAC wire to the LVTB blue term. And as long as I was up in the attic sweating, i moved the misplace blue wire from Y terminal to the blue term at the air hander and place the unused BR to the Y. Then moved appropriately at the stat (blue moved from Y2 to B, and hidden BR to the Y2). Cooling is running now, will switch over to heat soon for final test!

This was just in case anybody really wanted to know about another success story due to the PJ's help!

 

Thanks. It's important for me to know that my information was useful.