No C wire terminal on HVAC system


  #1  
Old 01-16-19, 02:06 PM
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No C wire terminal on HVAC system

Good afternoon,

I am trying to install a wifi thermostat. In a prior home, I was able to wire a C-Terminal on my Trane unit, but in my new house, the 30+ year old Payne Dualpac Rooftop unit does not have terminals. The existing thermostat has spare wires, I just need to know where I should wire one of them up to. I tried to switch the G wire to C on the thermostat which did allow the thermostat to turn on, but, when I try to turn on the heat or the AC, it doesn't work. In one thread, I read that I can add a wire to a screw next to where the red wire goes into the transformer at the top.

Any suggestions would be appreciated. Thanks.

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Last edited by PJmax; 01-16-19 at 03:24 PM. Reason: resized pictures/labeled second one
  #2  
Old 01-16-19, 03:05 PM
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If there is a transformer then there is a C terminal. From the pic I can't see the C on the transformer. What's the model number on the unit?
 
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Old 01-16-19, 03:26 PM
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Welcome to the forums.

You'll see I added labels to your picture. The wire at the top of the contactor will be your C wire. Follow it to where it goes. On that old unit...... C is more than likely the metal frame.
 
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Old 01-16-19, 03:43 PM
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Thank you for the warm welcome, and thank you both for the replies. Pete based on what you said could I just screw into the sheet-metal and attach the wire? What do you need to be in a certain place or can I just screw in anywhere?
 
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Old 01-16-19, 03:48 PM
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Did you follow the wire I labeled in pink as C ? Does it eventually go to the metal chassis ?
If it does.... you can connect your C wire anywhere there is an available screw.
 
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Old 01-16-19, 03:55 PM
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I will have to check when I get home tonight. I will follow up and let you know. Thanks for the guidance!

best regards,

Jeff
 
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Old 01-19-19, 11:21 AM
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Pete,

I checked the wire. It doesn’t goto the chassis. It goes into the two wire bunch that has the yellow piece joining two wires (arrow pointing at it) and then a black wire comes off and goes to a gas valve below.
 
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Old 01-19-19, 11:24 AM
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Here are the photos:
 
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Old 01-19-19, 11:26 AM
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I labeled the contactor in the picture. There are two contacts for the coil. One on top and one on the bottom. The one on the bottom we can see as yellow. I can't see the color of the top one I labeled as C. That top wire should be the C wire. That may also connect to the gas valve and it should eventually go to one of the transformer wires.

Maybe post another picture showing more of the contactor wiring.
I just saw your gas valve picture.
 
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Old 01-19-19, 11:27 AM
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Old 01-19-19, 11:30 AM
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Does the black wire in the above picture go directly into the transformer ?
If it does..... that is C.
 
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Old 01-19-19, 06:56 PM
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contactor picture...................

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Last edited by PJmax; 01-19-19 at 07:17 PM. Reason: resized/labeled picture
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Old 01-19-19, 07:16 PM
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Old 01-19-19, 07:20 PM
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It's the gray wire that I labeled C at the contactor. (post 8)
 
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Old 01-19-19, 07:21 PM
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Thanks for responding Pete. So, can I just add one of those clips to the end of my unused brown wire in the thermostat cable bundle and plug it into that part you marked as C?
 
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Old 01-19-19, 07:22 PM
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You can clip on to the contactor or follow that gray wire and connect anywhere along it.
 
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Old 01-19-19, 07:28 PM
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Thank you sir. I will try it out tomorrow and let you know how it goes.
 
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Old 01-20-19, 06:08 PM
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It worked Pete. Thank you for your guidance. You are a gentleman and a scholar!

Thank you!

 
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Old 01-20-19, 06:35 PM
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Good job. Back in business.
 
 

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