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Is the black wire 4 thermostat needed to make AC work ?

Grow LikeAPro
7 years ago

Curious situation I have here. I have a new central AC unit installed, I also bought the the new Nest thermostat, which needs constant power to stay charged for the WiFi signal to function.

History:

I had a black wire hooked to the O/B terminal on my old thermostat - Even though I had no heat pump or AC installed at that point in time.

I now have the an AC unit, and put that black wire on the O/B terminal of the Nest thermostat. Fine so far.


Everything works fine - however I keep getting a battery low error. I Google and find out that the Nest unit needs to have constant power, provided by a "c" wire. It seems that this black wire *may* be the "c" wire, but I'm unsure.

Tonight, I removed the black wire from the Nest thermostat for a test, and tried to turn the central AC unit ON, but it didn't work. So at this point I'm confused..... what is this wire doing ? and is it possible to move this wire to the "C" location for power ?

It seems this black wire is needed to somehow tell the central AC unit to turn ON.

This is confusing, if anyone has time, can they help me out, thanks much in advance.

Note: - I do NOT have any BLUE wire ( which is used for that "C" input )

My cable coming out of the wall has 5 wires:

Black, Green, Red, White, Orange.



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