C wire needed for new thermostat

7 years ago

Hi guys,

i just purchased an ecobee 3 wifi thermostat. When i went to install it i realized i needed to add a C wire. Ecobee thermostat even comes with an adaptor to help with this issue. My Problem is that my AC unit is located on my roof and not easy for me to get to. So i was looking for any other solutions before i decided to get a profrssional or just scrap the wifi thermostat.

i came across a 24 volt C wire adaptor that plugs into an outlet. Last night i tried to install the Ecobee with the adaptor. I have 3 wires coming from my wall, RC, Y and G. It is an air only system. It looks like the old thermostat had a jumper between rh and rc. I connected one of the wirrs from the adaptor the The C terminal And the other to the RH. The directions for the adaptor appear to show the second wire going to the RC terminal but since the R coming from my wall already occupied that terminal i improvised. I was able to fire up the themostat however when i attempted to lower the temperature to trigger the Air nothing happened. Ive tried googling and reading different diagrams to help me however i am having trouble finding a diagram that has the setup i do (R, Y and G coming from the wall).

At this point im starting to wonder if the adaptor would work with my setup. I figured i would try and get some help/advice before going any further. Any help would be greatly appreciated.

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Comments (3)

mike_home
7 years ago
Did you keep the jumper between Rh and Rc? Did you disconnect the original wire from from the wall and going to the Rc terminal?
Mike Brino
Original Author
7 years ago
the old thermostat had a jumper built in. When i was reading about the ecobee it said to remove the jumper so i did not run a jumper from rh to rc.

As for the second part of the question im not sure i understand. maybe this will help. The R wire coming from my wall i connected to RC on the ecobee. I connected Y to Y and G to G. i then connected one of the wires from the adaptor to the C terminal and the other wire to the RH terminal. And again i did not use a jumper from RH to RC. Hopefully this helps explain it better. Thank you for your help.
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mike_home
7 years ago
The Rh is to power the thermostat for heating, and the Rc is the power for cooling. Since this is a cooling only application, you only need a connection to the Rc terminal. Do not connect the old R wire from the wall to either of the adapter wires.

You need to disconnect the old R wire from the Rc terminal, and connect one of the adapter wires. The other adapter wire goes to the C terminal. The old R wire could be connected to Rh without the jumper, or keep it disconnected and cover the end with tape so it cannot short to any other wire. I recommend you keep it disconnected and covered.

If that does not work, then you may have to install the jumper between Rh and Rc. Consult the Ecobee installation manual about the wiring for applications that are cooling only.