C wire question


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Old 11-23-14, 07:04 AM
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C wire question

Getting ready to install Wi-Fi t-stat, and it needs a C wire. I took off the existing t-stat and found I do have the 5th wire there but not currently used.

Per the pics below, please help me out with the following:

1. Is it safe to splice an additional length of cable to reach the 24V transformer.

2. Which screw should I connect the blue wire to once I have extended it.

I'm pretty sure I can handle the rest from there.

PS: Looking to install Ecobee 3 (if that matters).





Thanks.
 
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Old 11-23-14, 08:44 AM
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It looks like the one transformer lead is connected to ground. You can connect your C wire to ground at any clean shiny metal location.

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Old 11-23-14, 01:16 PM
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Thanks, PJ....so basically the C wire is a ground wire......I can splice from the blue piece that is curled on the first pic right to any of the locations you point out and that should complete the circuit once I hook up on the C terminal on the new stat, correct ?.
 
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Old 11-23-14, 01:18 PM
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Correct .
 
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Old 11-23-14, 02:19 PM
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Are those blue wires connected to the metal box?
Geo
 
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Old 11-26-14, 07:42 AM
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Here is a better look....

Wire (A) goes from transformer to chasis...
Wire (B) goes from transformer to board....
Wire (C) goes from transformer up into furnace....
Wire (D) looks like ground for the A/C ?.


Not sure what wire C does ?

Seems pretty obvious that the common wire from the t-stat should connect to where (A) is now, so I am planning to extend to that spot.....unless someone calls out something different.

 
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Old 11-26-14, 08:05 AM
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"A" will work. You might consider connecting it at the wire nut circled in white in the attached photo if it would make it easier to access. That is the "C" wire connection that goes outside to the condenser.
 
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Old 11-26-14, 08:41 AM
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that makes a lot of sense and may save me the splice....thanks !
 
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Old 05-21-15, 11:54 AM
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Hey - sorry to revive this again but just now getting around to this........if I remove that wire nut circled and put a volt meter on it, what should I expect to see ?. 24V ?.
 
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Old 05-21-15, 12:10 PM
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Before making any connections, be sure to turn off the power to the furnace. Failure to do so could result in a blown fuse, burned out transformer, burned out stat, or fried board.

You should see zero voltage from that wire connection to ground & 24 volts to R.
 
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Old 05-21-15, 02:04 PM
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Ok thanks, and one more question..........

Looking at my board, I don't see a connector for Yellow..........I only see R, G, W.......where would Y be ?

 
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Old 05-21-15, 10:32 PM
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Where have you been ?

Y is not connected on that board.
The Common wire to the compressor is the white circled connection.
The Y connection to the compressor is the yellow circled connection.


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Old 05-22-15, 01:19 PM
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Well, I gave up. Got a new regular programmable LUX TX9600 and the hell with C wires. It turned out the blue wire has no continuity. Good thing I tested it before I started. To run new wire, I basically have to open up the wall in my dining room. The old wire is stapled to the studs (verified visually), so no using one wire to pull the other. Who needs WiFi anyway. I'll probably live longer not obsessing on my phone about the temp in the house LOL. I set the swing for 1 degree on either side of the set point. That should accomplish what I wanted in the first place (less CPH).

Off to drink beer. Hope the new stat lasts.
 
 

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