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Discussion Starter · #1 ·
i had to take my stat loose today, to put up drywall. when i loosened the screws, i noticed the blue wire had broken loose. the furnace was working just fine. so idk if that wire was loose or i had broken it right then.

anyway. green, white, blue, red. what does each wire do ?
 

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I'm Your Huckleberry
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Not colors, terminals but on average it is the color connected to the corresponding terminal.


Terminal/ wire color
G-green wire (fan)
W-white wire (heat)
Y-blue wire (cooling) -had you had a yellow wire that may also (instead of blue) have been used for Y/cooling
R-red wire (24 volts.power)

Many times the blue is used as a common on digital stats but again, you'd have a different color wire, mostly yellow, connected to the Y terminal for cooling.
 

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I'm Your Huckleberry
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Btw, you should turn the breaker to the furnace off before doing any stat wire work. You can blow a fuse or a transformer if you touch that red/power wire live to metal.
 

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I'm Your Huckleberry
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Now if you don't have cooling and you do have a digital stat than blue would be on the C terminal/common to power the stat.
 

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Roofmaster
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Plan Ahead

You do have a digital camera, or a cell phone with a camera in it, and took a picture or made a sketch of where the wires connected before you disconnected them right?

If the blue one broke, there should be a little wire loop under the screw where it went. Now at least you know where the blue one goes. ;-)
 

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Discussion Starter · #6 ·
ok

the red wire. that powers the stat ? my digital stat has batteries. so what does the red wire do here ?

i turned the furnace off with the switch on the side of it.

i did write down the connections. but i didn't need to. as the terminals are labeled.
 

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It brings 24 volts to the stat so when the stat closes one of its switches, 24 volts can be sent to the terminal that provides heating cooling or fan on, as needed.
 

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Discussion Starter · #8 ·
It brings 24 volts to the stat so when the stat closes one of its switches, 24 volts can be sent to the terminal that provides heating cooling or fan on, as needed.
thanx. yeah, i thought just that after i logged off yesterday.
 

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You didn't mention air conditioning so I'll assume you don't have that.

Some digital stats require (or have the option) of a connection back to the furnace that basically is the ground or neutral so the stat can use the power from the furnace's transformer to keep it powered up. This kind of style uses the battery only as a backup incase of a power outage.
 
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