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I'd like to start by saying I don't know much about HVAC (although a LOT more than I did before purchasing my ecobee). My home has 2 Heat pumps outside, an air handler (I think?) in the attic, and a furnace in the basement. I have a thermostat in my living room on the main floor, and in a bedroom on the top floor. I purchased two ecobee 4's- and have been using the one in the living room for months without much issue. However, the one upstairs does not have a c wire- forcing me to use the dreaded power extender.
My question is- where the heck do I install the extender? I looked at the air handler- there is no control board with labeled wires like there is on the furnace. There are colored wires, but they do not go into a control board with screws that I can easily remove/reattach to the extender. I took apart 3 different panels/coverings inside the air handler- which was about all that was visible, and never had a control board with labeled wires.
So now I am thinking maybe the extender needs to go to the control board on the furnace in the basement...? If so, will this not interfere with the other ecobee in my living room that is not using an extender? How do I identify which is which?
I noticed the furnace has a C, G, W, R, Y, and TWIN terminal- all of which have two wires connected except TWIN and G coming from two different "bundles" of wires. Obviously only one of these "bundles" has a G wire-which my upstairs Ecobee has connected- so does that mean the other bundle my other thermostat?
Let me know if I'm way off. I know thermostats aren't the only devices that use the control boards but I have no humidifier or any other equipment that I know of that would use it. Obviously it would help tremendously if I at least knew where the power extender should go for the second thermostat and then can probably figure out the rest.