:confused: :confused: :confused: :confused: :confused: :confused:

Well, I did a minor remodel for a business and part of that was to change out the thermostat for one that was a little more appealing to the eye. Did that and a few days later they said that the heater has not been working. At first I was getting about 18-20VAC off the red wire going out to the T-stat but then nothing. I was thinking that since I did not shut off the power to the furnace when doing the troubleshooting that I killed the transformer. I went and got another one and I think that I am wiring it correctly but I was hoping for a little reassurance/advice on how to wire it. Transformer has 2 yellows and one black on one side, and 2 blacks on the other. On the old transformer there was a black, red, and orange on one side and 2 yellows on the other. The furnace is a Trane and has become a pain. It does not help that I am not that familiar with HVAC and furnaces. Any help will be greatly appreciated. Thanks

Was one wire unused on the old transformer? If so, don't use the black on the side with the yellows. Connect the pair of blacks to the incoming 120, and the yellows to the board or wherever the old one connected. Except for the unused black, it doesn't matter which yellow is which, it is AC.