Please help find common wire on my furnace to power thermostat

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Old 02-09-16, 04:07 PM
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Please help find common wire on my furnace to power thermostat

Hi,

I got a new ecobee3 thermostat that requires a common C wire. In my thermostat wiring, I have an extra blue wire unused. I plan on using this blue wire to connect to the common wire in the furnace.


Could anyone help me? I thought in the picture of the blower diagram, is the "Wh common" is the wire to connect to? Any help is appreciated.!!


Thanks

Full image file of furnace: rheem furnace - Album on Imgur




 
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Old 02-09-16, 04:11 PM
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In my opinion, you need a multimeter and someone with the skill to use it to decide how to wire up your thermostat.

Just going on the color of the wire is an invitation to a problem. You need to check and be sure.
 
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Old 02-09-16, 04:18 PM
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Welcome to the forums.

Don't connect to anything yet. That COM you are talking about is the 120v neutral. You don't want to connect there.

This is what we are interested in. What are the four colored wires on that transformer.
White, black, ???, ???.

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There is usually a wiring diagram on the back of the blower door.
That transformer is not the original..... it's been added. The one on the fan center may have burned open.
 
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Old 02-09-16, 04:21 PM
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Thanks for the info. I thought I might be wrong since the wire is too thick... I thought I could do it myself but this old furnace is not helping to make it easy.
 
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Old 02-09-16, 04:28 PM
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No problem. I added to my post so go back and re-read it.
 
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