No C terminal on my air handler.


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Old 06-16-17, 06:25 PM
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No C terminal on my air handler.

I have an old Trane system (single stage heat pump) and want to install a WiFi thermostat, but need a "C" wire to power it.

There is no such terminal on my air handler. There is 24V across the red/blue and red/green terminals. Can I just install a jumper between either the blue or green and the C terminals?
 
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Old 06-17-17, 05:07 AM
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Can you post some pics of the transformer?
 
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Old 06-17-17, 08:51 AM
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Thanks for the reply.
I cannot get to the transformer w/o a major dismantle of the air handler, so I have attached a drawing of the connections.

There was also a schematic in the AH so I inserted the relevant portion of it into the drawing. As you can see, the blue and green wires come off one end of the transformer secondary and the red wire comes of the other.

I'm wondering if I can attach a C wire to the blue/green side.

Name:  HVAC Wiring.jpg
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(Not sure if I got the drawing attached. I'll post and see.)
 
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Old 06-17-17, 08:55 AM
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Looks like the picture posted. However the bottom was cropped a little. The box at the bottom shows the thermostat connections. The fine lines you see at W/Y and RC/RH at the are jumpers.

The box on the left is the air handler connections.
 
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Old 06-17-17, 09:07 AM
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Blue wire is the common. Green wire starts the blower.
 
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Old 06-17-17, 09:42 AM
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I have an unused wire (which happens to be blue, by the way) in the cable running to my thermostat. If the blue is the common, then I should be able to connect the AH end of the wire to the B terminal and the other to the C terminal on the Tstat. Correct?

BTW here is the entire schematic.

Name:  Air Handler Schematic.jpg
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Old 06-17-17, 11:16 AM
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Welcome to the forums.

On a Trane....B is the Common wire. You'll see it goes from the transformer right to the B terminal on the low voltage wiring strip.

Name:  Air Handler Schematic.jpg
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Old 06-17-17, 01:27 PM
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Got it!

Thank you Skaggsje & Pete.

My local utility is offering a rebate on Honeywell, Ecobee and Nest thermostats. I thought I'd take the opportunity to upgrade. Now I know I can do it.

John
 
 

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