Nest thermostat - wire identification

Old 02-25-14, 12:03 AM
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Nest thermostat - wire identification

Hi all,

I looked at many sites but couldn't sort my HVAC wires coding conclusively. I have the following wires where my old thermostat was:

White - heating
Yellow - cooling
Green - fan
Red - 24V power
Brown - ??
Light Blue - ??

I need help sorting out what the brown and blue wires are for. Thanks in advance.
Old 02-25-14, 08:09 PM
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Yellow, green, red and white are commonly used for the purpose that you have posted, but not always.

Brown and blue are not as standardized.

You need to look up the thermostat to determine the function of the terminals or remove the panel and identify the connection in the furnace to know with any certainty the function of your wires.

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