I have installed a Nest thermostat into a system with hot water heat and separate a/c system each with its own transformer. To run a C wire to gain constant power, does the wire connect to the boiler, a/c, or to both. Additionally, I would like to be able to disconnect the opposite system depending upon the season. Is this possible? Thanks
2 on boiler side; R to Rh and W1 back to zone valves. 3 from a/c; R to Rc, Y to Y1, and G to G. There are no designations on a/c terminal block but I am attaching schematic from documentation. I assume my terminal marked with arrow would correspond to C.
Easy. It is in the attic right above the thermo. I can go either way, also, since I can fish from boiler to attic, to thermo as well. Nest has never confirmed that with both Rc and Rh wired, the common wire connection for constant power is only between Rc and C which makes connecting to a/c the logical answer.