[danieltran]

Hi everybody,
I want to install a wifi thermostat (ecobee4) and I've done some researches of how to do it. My current thermostat doesn't have a C wire. The things that confuse me are:
_Why there is a jumper wire from R to Rc?
_At the control board, the Yellow wire connected to a Red wire from a different set of cable. And there is a White wire from that cable goes to the Com (C) terminal (pictures).
Could someone show me how to install the ecobee4 kit for the control board? Thank you very much for your help.

 

[yuri]

The jumper from R to RC is used when you are using a conventional furnace. With a boiler you would have a separate 24 volt transformer and another in a air handler/fan unit with AC and one thermostat/tstat could operate both.

Leave it alone on the new tstat also.

I suspect your tstat wires going upstairs are spliced in to the wiring from the board further down the road and that is why it looks different.

All you have to do is run a wire from the board to the new tstat and hook it up to C on the board. The AC is spliced into the wiring downstream and OK.

 

[57TinkerMan]

Looks like you have some extra wires.

 

[diyorpay]

My opinion under original post in Appliances

 

[danieltran]

Thank you all for your help.