What wire do I connect to 24Vac common on thermostat?

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Old 10-15-09, 05:58 AM
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Question What wire do I connect to 24Vac common on thermostat?

Hello,

I have installed a honeywell thermostat model TH8320U and would like to use the 24 Vac Common Wire to power the unit as opposed to using AAA batteries. I've read through some posts here and for the most part there is a blue wire that usually connectes to the C screw. In my case, I only have Red, Green, Black, and a beige almost white coloured wires that connects to my unit.

Of those wires which one do I connect to the 24Vac C screw to send power to the unit?

Our home is newly built with high efficency gas furnace and ac.

Thanks in advance.
 
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Old 10-15-09, 09:09 AM
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Your thermostat cable does not have a common wire, so you'll have to either pull a new cable or stick with the batteries.

If you wanted to sacrifice the ability to control the fan separately (which many people don't use), you could re-purpose the green wire. You would need to rewire it at the furnace end to the common terminal on the transformer then you could use it to power the thermostat.
 
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Old 10-15-09, 11:04 AM
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Originally Posted by ibpooks View Post
Your thermostat cable does not have a common wire, so you'll have to either pull a new cable or stick with the batteries....
Thanks for your reply. When you say pull a new cable, do you mean wire a cable from the furnace, up into the wall where the thermostat resides, or split it off from an existing wire?
 
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Old 10-15-09, 12:12 PM
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I mean install a new cable from the thermostat to the furnace. The old cable would be abandoned.
 
 

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