Hello, I just picked up a Honeywell RTH6580WF to run my Criterion II gas furnace and Lenox AC Unit. I like that the unit can remotely adjust the temperature while I am upstairs. I also thought for those in between days it would be nice to set it up so that when it a cold morning the heat will come on, but then in the afternoon when it gets warm the ac will automatically come on to keep the house relatively the same temp.

The Honeywell unit requires a C wire connection to operate correctly. If you do not have a C wire with your setup you can wire it using an alternate method outlined in this video Honeywell DIY Wi-Fi Thermostat Substitute G-Wire for C-Wire-- US and Canada - YouTube Basically the video says to move the G wire on the thermostat side to the C and then on the furnace side to swap the G wire to C and then put a jumper from Y to C. By doing this I loose the option of turning just the blower fan on by itself. I occasionally do like to run the fan alone, especially with the AC since it seems to help even the upstairs and downstairs temperature some.

My question is...can I leave the G wires connected like they were (G on both ends) and then use one of the many extra wires I have in the thermostat wire bundle to connect to the C on the furnace and the C on the thermostat? That way I can run the blower fan by itself.

Also, would there be a way to wire it so that the Auto Heat/Cool function would work with this setup?

Below are some pics of my wiring. There are some extra wires in the pics that go to the AC condensation pump and the AC unit itself. They are red and white two wire bundles.
Thanks!
DAVE

 

Connect your unused blue wire to "C" at the stat and at the furnace.

That video was an option for those that only have 4 wires to the stat and do not want to pull new wire.

Set option 12 to 1 to enable the Auto changeover Mode.

https://customer.honeywell.com/resou.../69-2718EF.pdf

 

[SUP]excellent. Thank you very much![/SUP]