Heating & Air Conditioning Electrical Wiring

Installing Ecobee Thermostat

5 years ago

I see on the control board of my furnace I have a C Wire but it's not going up to the existing thermostat. The C and one of the Y wires are going to what looks like is a spliced in electrical box.

Where could I go from here?

I installed the same thermostat at a friends who didn't have a C wire but there was an extra at the furnace and the thermostat location so I just connected one end to the board and other at the thermostat. I'm not sure why I would have some wires trailing off to a electrical box. Thank you

Featured Answer

mike_home

5 years ago

The simplest solution is to use the extra wire as the C connection.

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Comments (6)

wdccruise
5 years ago
"The C and one of the Y wires are going to what looks like is a spliced in electrical box."

Not understandable.
stew930
Original Author
5 years ago

The white C and the red Y are going to an electrical box shown.
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mike_home
5 years ago
Are you sure the red wire is the one connected to Y and not the one connected to the R terminal? If it is the R and C terminals, then this electrical box may be connected to the 24 V transformer which would make sense.

Do you have a voltmeter? If you do take some measurements starting at that box.
wdccruise
5 years ago
It looks like you need to follow the Ecobee instructions. I don't know which model Ecobee you have, but the Ecobee E4 installation instructions (for example) describe how to install this Ecobee thermostat when the old thermostat had only 3 wires and no C wire.
stew930
Original Author
5 years ago
I did test two cables and they are 24V.

I do have an extra wire on both ends. I assume I can connect that to the C connector on the board and the other end to my Ecobee?

I have a Y, W, G, and RH and a spare wire at the thermostat.