Help locating 24VAC common wire on Trane Air Handler

Old 08-31-14, 06:55 PM
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Help locating 24VAC common wire on Trane Air Handler

Hi, I have a Trane Air Handler (2tc3f60) and am tryign to connect a new wifi thermostat to it

original thermostat only has 4 wires (red green, yellow and white)

new one says it requires 24vac common wire in order to function

I read that this should be on the transformer in the air handler

I found a blue wire not connected at the air handler but have no idea which is the 24vac common

I tired the blue wire metered out tot he red wire on multimeter and it did not produce 24volts

any advice gratefully received, I have attached pics of air handler wiring below, can take more if needed


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Old 08-31-14, 07:23 PM
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It's hard to tell from the pic. Can you post a pic of the wiring diagram?
Old 09-01-14, 01:42 PM
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On a Trane system the common wire is designated as B. The white plug with six wires at the top right of your first photo (and the attached photo) contain the 24V red wire and the 24V blue wire (common). If you set your multimeter to volts AC you should get a reading of 24VAC between them. The blue wire with the wire nut is the wire you want to use to power the C terminal on your new thermostat. Make sure you turn off power to the air handler before making any wiring changes. If you have any additional questions please post back. I attached a photo that shows the red wire and blue wires that come from the fan relay that powers the low voltage side of your system and the blower motor.
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