Nest Thermostat Dual System

sphelps81

I have a dual transformer systems and bought a 24 volt c wire adapter since i do not have a c wire. my rh and rc terminals are in use. with the adapter can I put one of the wires with the rc wire terminal and then the other to the c. If I put the rc wire that’s already there with the adapter wire will it hurt anything? Its currently running fine that way.

109A_5

The NEST may not care where it gets its 24VAC power from, Rc to C or Rh to C as long as it gets a constant 24VAC power. Also if you look at your HVAC equipment the individual wires to the thermostat's Rc and Rh terminals may be wired together to an R terminal there.

sphelps81

So if I put the adapter wire from the 24volt in with the existing Rc wire it shouldn’t hurt my air unit then?

GW

If it were me, I would skip the Rh, and use that wire for a C, and then install a simple relay control at the cooling equipment to operate the heating system.
 Of course, I don’t know where these wires are going, so that idea may not work well. If the heating and cooling equipment is next to each other, this would be relatively simple. If you have some basic wiring skills. It’s low voltage, harmless