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Discussion Starter #21
IF, cable 1 goes to compressor... and
there's another cable, cable 2,...
is that where the mystery wires to thermostat are?
Just a guess.
Yellow Brown and blue are at the air handler.
there are yellow brown and blue wires at the thermostat. (brown is just capped off with a black wire). brown wire has the same labeling as the one coming from the air handler. So i'm pretty sure those are all the same wires.

So the only things that don't make sense is
1. where did the extra yellow wire come from at the thermostat
2. where did this orange come from?
3 why are the brown and new black wire capped together?
 

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Just guessing here, you live in a warm/warmer climate, you don't have electric heat elements in the air handler, you do have a heat pump and the air handler wires and thermostat wires make their junction in the condensing unit instead of the air handler. Take a close up picture of the wiring diagram on the air handler and post it, that will help.
 

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Discussion Starter #25
Just guessing here, you live in a warm/warmer climate, you don't have electric heat elements in the air handler, you do have a heat pump and the air handler wires and thermostat wires make their junction in the condensing unit instead of the air handler. Take a close up picture of the wiring diagram on the air handler and post it, that will help.
Here's the wiring diagram
 

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Your orange cable goes on the 'B' Nest terminal? It was on original thermostat on 'O' terminal. It's 'O' or 'B' dependent upon brand on main unit.
 

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We need to agree what Brown and Black wires are that are twisted together at old thermostat. They are bypassing old thermostat and going elsewhere.
May be time for a meter reading to see which supplies 24V constant.

Suggest a pigtail from under cap (a third wire) same thickness if possible, to 'C' terminal on Nest.

Alternate method requires another transformer or bridge to supply 24V to Nest. We want to find it in existing wiring.
 

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Discussion Starter #30
So I can install it like this, but this will lead to problems like others have mentioned about the power.
To truly install it and make sure it right I would need to find out if the black wire closes the power loop with the R (yellow wire) with a meter.
or find another way to get a c-wire
 

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So, the B terminal in your air handler is common. You need to find/run a wire from there to the thermostat C terminal. Or find/run a wire from the condensing unit where the B wire connects and to the thermostat C terminal.
 

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Discussion Starter #32
So, the B terminal in your air handler is common. You need to find/run a wire from there to the thermostat C terminal.
Yeah, I'm pretty sure this is the same brown wire, but I don't know what this black wire is that it is capped off with at the thermostat
 

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Discussion Starter #33
We need to agree what Brown and Black wires are that are twisted together at old thermostat. They are bypassing old thermostat and going elsewhere.
May be time for a meter reading to see which supplies 24V constant.

Suggest a pigtail from under cap (a third wire) same thickness if possible, to 'C' terminal on Nest.

Alternate method requires another transformer or bridge to supply 24V to Nest. We want to find it in existing wiring.

Yeah, I could use the cable the was the bridge on the y/w on the old thermostat, but would this effect whatever the black cable is doing?
 

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I feel that's the one you want as 'C'.
I would pigtail it because if it goes off with the black to somewhere else (likely the compressor that also needs a 24V constant) it's still what you need at the thermostat.
 

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Looks like you have a bunch of wires in the T-stat box. Maybe that's the junction you are looking for. Pull them out and see what you have, post pic.
 

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Discussion Starter #38
Alright!

It's on and it read the wires it seems like its working, BUT it feels like hot air when I press AC and cold air when I select heater???
 

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Discussion Starter #39
Fixed it. I just picked the wrong seating after heat pump. I picked B because that's what mines was but it's auto set to O. Switched it and we're good to go fam. No extra wires needed, no add a wire and no using the g wire. Got fully function heat, cold and fan! Thanks for all your help this was a fun DIY.
 

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