01-01-2022 03:30 PM
When selecting a thermostat, I had three choices, ecobee, Sensi, and Nest. The ecobee and sensi both required a C-wire, the Nest advertised that it doesn't. The ecobee and sensi systems have an alternative that allows a power converter to be added to the control board of the furnace. My furnace does not have a control board, so installation isn't that easy and it made my system seem incompatible with both.
Having gone with the nest, and realizing the false advertising has led me astray, I will need to provide a C-wire to get the unit to function properly. Having a furnace that doesn't use a control board, none of the after market converters seem to work on furnaces that don't have a control board.
My system has a 120/24 transformer, a relay, and a gas valve - that's it. Is it possible to add a wire from the other side of the 24 VAC transformer that runs the control relay? Is the C-wire simply 24 VAC, or something else? If it's just 24 VAC, would one leg of the transformer go to the Rh - power, and the other leg go to the C terminal?
What's the current draw from the thermostat? I don't think it would be more Volts/Amps then the transformer can handle, but I want to double check first.
My system is a forced air, heat and cool. Thermostat is Nest Learning, 3rd Gen.
Wires used are RH - power, W1 - heat, Y1 - cool, G - fan.
Thank you, happy new year.
01-02-2022 07:49 PM
Yes, the C wire is from the other side of the 24v transformer.
Where do the Rh, W1, Y1 and G wires connect where your furnace and A/C are located? If you have a fairly traditional system with an outside A/C compressor, you would also have a 2-wire bundle coming in, with one wire connected to your Y1 terminal, and the other wire in that bundle goes to the C or 'other' side of the 24v transformer. Run a wire from there to the C in your Nest.