How to wire in 24vac auxiliary power for thermostat

383bigblock · 04-12-2010, 06:20 PM

Hello All,
I just purchased a Honeywell Vision Pro 8000 and don't want to rely on AAA batteries to keep it running. I have the standard 1H/1C system. I have everything working. Here's the question. The RH is coming from my heater to the RH terminal on the thermostat which is also jumpered to RC (although I have nothing coming from the cooling system to it). I want to install a 24vac power supply to run the thermostat without batteries. I believe I can hook the 24vac common to the "C" terminal on the thermostat, but do I hook the 24vac hot to the RC terminal and remove the jumper between it and RH????. I read somewhere that this will work but you need to unjumper it to keep from messing up the RH circuit on the heating unit's board. Has anyone done this before and is it that simple.

Thanks in advance. I just don't want to screw up the circuit board of my heater that is providing the RH circuit.

Michael

**beenthere** · 04-12-2010, 07:56 PM

That will work(must remove jumper).

Its the hard way. Should have just used the common from your furnace.

biggles · 04-12-2010, 09:18 PM

the Rc-Rh is a constant 24Vs if you connect the C on the subbase to the C of the TR...bateeries are for backup only to default and hold settings.....i thought all electronic stats out there call for R-C 24v constantly on the subbases...to support the VA of the stat.......

**beenthere** · 04-12-2010, 10:32 PM

Quote:

Originally Posted by biggles

the Rc-Rh is a constant 24Vs if you connect the C on the subbase to the C of the TR...bateeries are for backup only to default and hold settings.....i thought all electronic stats out there call for R-C 24v constantly on the subbases...to support the VA of the stat.......

No, lots of stats are still able to operate by battery, or 24 volts.

biggles · 04-13-2010, 08:04 AM

that TR within the furnace is the power source for the cooling condenser thats why there is a jumper on Rc-Rh on the subbase just connect C....use the AAAs for something else

383bigblock · 04-13-2010, 08:10 AM

BeenThere,

Thanks for the information. I would rather not run a separate 24vac transformer to power the unit. Right now RH is coming from my furnace to the Bridged RH/RC connection. Are you saying I can go back to the furnace and grab a "common" terminal and run a line from it to my "C" terminal on the thermostat and that will accomplish the same effect without needing a separate power source? If that is the case that would be awesome.

Michael

**beenthere** · 04-13-2010, 08:13 AM

Yes. Thats how most thermostats are done.

Your furnace control board should have a "C" terminal on it.

If not, you can wire the thermostats C terminal directly to the transformer's common.

Then your batteries are just back up.