Honeywell installation - C Wire

9 years ago

I bought the Honeywell WiFi Smart Thermostat and started trying to connect it to the system in my home. I have never done anything quite like this before.

My current Thermostat has G Y W and RC wires with a jumper to the RH connection from the RC.

The Honeywell has W Y G N2 Y2 C K RC and R connections

From what I was reading online I need to run the Y and W to the corresponding connections, RC goes to RC and I need a jumper to the R, and the G wire should go to the C connection.... This is where it gets confusing to me:

Now it says to go out to the heating system and on the board in there I need to move the G wire to the C connection and run a jumper wire from the Y to the G connection so that the fan will run... which is fine except that the board out there has G R Y W and Com (24v) connections. Jumping the Y to the G is no big deal, but is the Com (24v) the same as just the 'C' connection? (see below for pic)

Any help figuring this out would help me a ton.

Thanks!

Greg

Comments (3)

mike_home
9 years ago
The Com terminal is the common or ground side of the 24V transformer. It is the C connection (C = Common).

Do you have a spare wire in the bundle of wires? If you do should use the extra wire to make the C connection.

Be aware you will loose the ability to turn on the fan when the furnace is not running if you use the G wire.
GregB42
Original Author
9 years ago
I have 1 extra wire, that blue one in this pic that is tucked back around behind the rest. I dont know where it goes... I will go look outside again when I get home but I didnt see it out there. If I can find the other end of it I will use it for the C.

We asked an HVac tech to help us learn how to use our current one, he messed with it for about 15 min and gave up just telling us it was junk and to get a new one so that is what we are doing.

Thanks :)
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weedmeister
9 years ago
Guessing this is not a heat pump system? For HPs, the blue traditionally is used for the reversing valve. If this is normal AC, then it would be an extra and useful here.

Put G to G. W to W. Y to Y.

The Honeywell instructions should tell you whether you need to jumper R and Rc.

(More information than you need: For homes that have separate heating and cooling systems, there are Rh and Rc. Two transformers, two hots.)

Then take that unused blue wire and connect it to the Com on the furnace and the C on the Honeywell and see what happens.