I’m trying to add c wire to furnace to run a WiFi thermostat but don’t know where to hook up c wire to get power to turn on thermostat i have 2 extra wires just don’t know where to put one them to get power
Wiring – Adding C wire to WiFi thermostat
installationthermostat-c-wirewifiwiring
Related Solutions
There should be no problem connecting the C wire from your thermostat to the C terminal in the furnace. Take a look at this diagram, which is a rough approximation of your system.
Notice the cable going to the condensing unit has a red wire connected to the Y terminal in the furnace, and a white wire attached to the C terminal. When the thermostat calls for COOL, it does so by energizing the Y terminal (connecting R to Y). This provides power to the coil of the contactor, which allows it to close the contacts and turn the condensing unit on. The other side of the contactor coil is connected to the C terminal, as to provide a complete circuit.
You'll notice in the first image that two relays in the furnace, the thermostat, and the contactor coil all connect to the same leg of the transformer. This is because the thermostat basically works like a switch, connecting the R wire to the C wire through control circuitry. Anything that needs 24VAC power, will be connected to both legs of the transformer.
I just got off the phone with Honeywell. If you only have a 4-wire older system, you'll only be able to use the fan in the "auto" position. It won't let you use the fan-only selection. You need a 5th wire for power for the wi-fi side of the thermostat. Call Honeywell and they'll walk you through it for free.
Best Answer
Look for the junction of brown wires and attach your C wire to that
On the wiring diagram for your furnace, the brown wires are all C wires, and they come together at a junction that should be somewhere near where the mains wires come in. Connect your C wire (which can be any unused wire in the thermostat cable) to that junction, perhaps with a length of extension wire (brown stranded #14 THHN/AWM will do the trick), and you'll be good to go.