https://www.googlenestcommunity.com/t5/Nest-Thermostats/Advertised-as-works-without-a-C-Wire-not-the-case-How-to-add-to-an-old/m-p/74793#M16712 <P>Yes, the C wire is from the other side of the 24v transformer.&nbsp;&nbsp;</P><P>Where do the Rh, W1, Y1 and G wires connect where your furnace and A/C are located?&nbsp; 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.&nbsp; Run a wire from there to the C in your Nest.</P> Mon, 03 Jan 2022 03:49:03 GMT johnCNA 2022-01-03T03:49:03Z https://www.googlenestcommunity.com/t5/Nest-Thermostats/Advertised-as-works-without-a-C-Wire-not-the-case-How-to-add-to-an-old/m-p/74282#M16584 <P>When selecting a thermostat, I had three choices, ecobee, Sensi, and Nest.&nbsp; The ecobee and sensi both required a C-wire, the Nest advertised that it doesn't.&nbsp; The ecobee and sensi systems have an alternative that allows a power converter to be added to the control board of the furnace.&nbsp; My furnace does not have a control board, so installation isn't that easy and it made my system seem incompatible with both.</P><P>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.&nbsp; 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.</P><P>My system has a 120/24 transformer, a relay, and a gas valve - that's it.&nbsp; Is it possible to add a wire from the other side of the 24 VAC transformer that runs the control relay?&nbsp; Is the C-wire simply 24 VAC, or something else?&nbsp; 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?</P><P>What's the current draw from the thermostat?&nbsp; I don't think it would be more Volts/Amps then the transformer can handle, but I want to double check first.</P><P>My system is a forced air, heat and cool.&nbsp; Thermostat is Nest Learning, 3rd Gen.</P><P>Wires used are RH - power, W1 - heat, Y1 - cool, G - fan.</P><P>Thank you, happy new year.</P> Sat, 01 Jan 2022 23:30:58 GMT https://www.googlenestcommunity.com/t5/Nest-Thermostats/Advertised-as-works-without-a-C-Wire-not-the-case-How-to-add-to-an-old/m-p/74282#M16584 JTB 2022-01-01T23:30:58Z https://www.googlenestcommunity.com/t5/Nest-Thermostats/Advertised-as-works-without-a-C-Wire-not-the-case-How-to-add-to-an-old/m-p/74793#M16712 <P>Yes, the C wire is from the other side of the 24v transformer.&nbsp;&nbsp;</P><P>Where do the Rh, W1, Y1 and G wires connect where your furnace and A/C are located?&nbsp; 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.&nbsp; Run a wire from there to the C in your Nest.</P> Mon, 03 Jan 2022 03:49:03 GMT https://www.googlenestcommunity.com/t5/Nest-Thermostats/Advertised-as-works-without-a-C-Wire-not-the-case-How-to-add-to-an-old/m-p/74793#M16712 johnCNA 2022-01-03T03:49:03Z