Yet another 'C' wire question

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Old 05-24-19, 05:04 PM
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Yet another 'C' wire question

I'm installing an Ecobee3 Lite. The air handler doesn't have a C terminal and the current stat has 3 wires coming in - R, Y and G. (There is a boiler for heat currently on a separate stat which I'll wire to the new Ecobee). I get voltage across R and Y, and R and G. Can I jump either G or Y to C at the Ecobee to complete circuit? Or will that foul something up? I can add in a transformer easily enough if need be. Thanks for any thoughts!
 
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Old 05-24-19, 05:31 PM
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If you're going to use that stat to run a separate A/C and heat plant..... you should get a C connection from the air handler. You may not see a C connection but it's there.
 
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Old 05-24-19, 06:04 PM
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Thanks for answering. Yes, that's what I expected. I checked for voltage across from R to the other terminals...hoping that was the correct way to find it? Terminals are R, O, G, T, B, W1, W2, Y on the handler. R, G and Y go to stat, Y and B go to condensing unit from the handler.
 
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Old 05-24-19, 06:15 PM
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If it's a Trane...... B is the common/C.
 
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Old 05-24-19, 06:25 PM
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Thanks, Pete, I'll climb up there tomorrow (it's in a small attic) and see if I can get a reading. The terminal screw is a bit rusted, so maybe that was a problem on my first try. Not sure of the brand as I didn't see a label on the side that is accessible.
 
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Old 05-24-19, 06:31 PM
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The condenser requires 24v to operate and it gets the 24v from Y and the common from B.
 
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Old 05-24-19, 07:34 PM
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Right! B has to be common. My brain must be running on less than 24v not to see that...thanks!
 
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Old 05-25-19, 08:57 AM
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Worked like a charm...thanks, Pete
 
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