Need help locating 24 VAC for C wire on old furnace.


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Old 01-04-15, 06:00 PM
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Need help locating 24 VAC for C wire on old furnace.

Sorry to post another c wire question, but I can't figure mine out regardless of how many threads I read. I'm upgrading my stat to a wifi one and need a c wire. My system is heat only, and is currently running with only two wires, red wire to Rh, and white wire to G. I have extra wires available for use, but can't figure out where to connect on the furnace end.

The red wire goes to what I think is a transformer (first picture). The white wire pigtails to a grey wire, which then runs to the TH terminal on the ignition control unit (second picture). The third picture may not be pertinent, but I added it since it was in the middle of everything else.
 
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Old 01-04-15, 06:50 PM
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Common is the transformer terminal with a black wire on it...
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Old 01-04-15, 08:06 PM
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I wired the stat using that location for my c wire, and it worked to supply power to the stat. However, my heat will not turn on now. The pilot has gone out and will not start back up. This has never happened before. I am now undoing everything to see if it works with the old setup.

**Edit**
The old setup works fine.
 
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Old 01-04-15, 09:14 PM
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Pilot..... I don't think your furnace has a pilot light.... at least not a standing pilot light. It may light when the module tells it to via spark ignition.

At your thermostat..... if you have an Rc and Rh ..... put a jumper across the two and connect the red to one of them.
 
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Old 01-04-15, 10:22 PM
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Did you connect Blue to C at the stat and at the transformer, connect Red to R and Rc at the stat, and connect White to W at the stat?
 
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Old 01-05-15, 05:11 AM
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My white wire is the one that pigtails to a grey wire at the furnace and connects to a "grey" terminal. On my old stat, this wire was run to G. I connected it to G on the new stat, but that didn't work. I moved that wire to W and it now works. Is it ok that a G wire is going to W on the stat?

Thanks for the help guys! I really appreciate it!

Nick
 
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Old 01-05-15, 05:30 AM
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G is energized for fan
W is heat signal
R is 24volt power
C is 24 volt common
Y is energized to run a compressor.

White should connect to W but I can see G working if the stat was configured for electric heat. Putting the fan switch to the ON position would never allow the heat to turn off that way though. I would definitely connect to W.
 
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Old 01-05-15, 05:31 AM
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If it is working it's fine ,but the normal configuration would be R on Red. W on white, Green on G,just makes it easier to troubleshoot in the future.
Geo
 
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Old 01-05-15, 07:23 AM
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Probably will not want to connect anything to G in this application.
 
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Old 01-05-15, 08:38 AM
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Great. Well, it's working perfectly, so I'm happy.

Thanks again.
 
 

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