I know how to make it work without the extra wire BUT it is far to much of a risk of damage if not done properly. That is why I said there is a need for an additional wire. If I am not comfortable with the posters knowledge base in the HVAC trade I just do not pass along all the information. It is easier for them to just run another wire and be safe. Been there done that got the shirt and the hat.

I am done with this post. I shall replace the battery once a year or as required. I am enjoying this cadillac and I do not want to ruin it.

Cheers,
Eric.

I am sure you will get buy with the battery operation and someday you never know you might just run that additional wire. If you do post back for the hookup.

hvac1000,
There are some features of the unit that require 24Vac to the common C terminal. I have just decided not to use those features. Just a matter of curiosity, what is involved to have power to the C terminal without running extra wire? This knowledge won't hurt.


Thanks,
Eric.

You have to power balance the transformers and change the wiring. It can get real tricky to say the least. It is not forgiving and one false move and the wiring,thermostat and transformers will be all toast.

ANother product which has a niche market is something called Add-a-wire. It allows running "an extra wire" withut physically running one. A small gizmo is placed in the wall behind the stat and another at the furnace. It "creates" the extra wires.

Oh, and BTW there is a version of the Vision Pro stat which only requires 3 wires. It communicates to a box installed in the furnace that contains all of the relays of the stat. So, you can have your cake and eat it too, so to speak.

Buy Honeywell VisionPro IAQ Programmable Universal Thermostat with Outdoor Sensor | Honeywell YTH9421C1010

Yep the add a wire is available BUT he does not want to add a signal wire he wants to add a neutral power wire. You would have to adapt one of the signal wires into the add a wire split then use the left over wire for the neutral/common - power conductor. That would be interesting. LOL

I am done on this. Thanks all. You guys are great.

Cheers,
Eric.