Thermostat wiring


Old 04-06-18, 07:30 AM
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Exclamation Thermostat wiring

I bought a nest several months ago and after about a month it stopped working. Looked like the battery had been discharged and was not charging back up.
I had a look at my wiring inside the house and there is one bundle of wiring coming from the hvac unit outside. However, when i go out side to look at the HVAC unit it appears that the C wire, which I read is the one that will charge a powered thermostat, appears to be hooked up to a second bundle of wires.

Inside the house I was attaching the blue wire to the C , but I can see outside that there are no attached blue wires. There is a second red from a second bundle of wires attached to the C with another white wire attached to the Y. It appears I would need to disconnect the second red from the second bundle of wires and connect the blue. However, I am not sure if that will cause a problem, or why their is a second white attached to the Y terminal.

As an additional note, the upstairs unit is wired the exact same way.

i have included pictures that have been labeled. I am a newbie here and appreciate any help.

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Last edited by PJmax; 04-06-18 at 10:02 AM. Reason: added and labeled pic from link
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Old 04-06-18, 10:06 AM
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Welcome to the forums.

You'll see I added a picture to your post. I've labeled the cables. One to the thermostat and the other to the outside A/C condenser. The condenser only needs to wires to operate...... C and a Y.

I also pointed to the blue wire in the stat cable. This is the blue wire that goes to your stat. It needs to be connected to C along with the red wire that is currently there.
Old 04-06-18, 11:49 AM
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Fantastic, I was hoping it would be something simple like that.

I will give it a try as soon as I get home tonight.

Thanks for your help

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