We want to install a smart thermostat and need the C wire. The wire is there but is not connected to our current thermostat. I checked in the furnace and none of the extra wires that go to the thermostat is connected to the C terminal.
There are currently 2 wires connected to the C terminal: one coming from the A/C and the other one is the humidifier. If I connect the blue wire to the thermostat and then the blue wire from the thermostat line to the C terminal in the furnace (i.e. the 3 wires in the connector), the furnace does not work and the circuit board has the idle code message. I get the same result if I use a pigtail or not.
If I connect only the blue wire in the furnace and in the thermostat, I see that the thermostat gets the power.
I do not know why it does not work when the 3 wires are connected to the C.
I have attached the diagram of the current connection. The difference with this diagram and my connections is that there is also a humidifier that connects to the C and W terminal of the furnace board. Thanks for your assistance.
It wouldn't matter how many wires connect to the common terminal in the furnace the thermostat would only require one of them.
That diagram is for the Vanee HRV interlock. It sounds like you are using the wrong common wire coming from the HRV.
Just connect whatever color wire you connected to the thermostat C terminal directly to the C terminal in the furnace. You should not need to put it in the marrette with other wires.
Are you trying to replace your HRV control with a new thermostat?
Quote from: Admin on November 28, 2022, 06:04:28 PMIt wouldn't matter how many wires connect to the common terminal in the furnace the thermostat would only require one of them.
That diagram is for the Vanee HRV interlock. It sounds like you are using the wrong common wire coming from the HRV.
Just connect whatever color wire you connected to the thermostat C terminal directly to the C terminal in the furnace. You should not need to put it in the marrette with other wires.
Are you trying to replace your HRV control with a new thermostat?
Thanks for your answer. This is the current connection with the existing thermostat (Honeywell programmable (TH4110U2005) and existing Vanee HRV. I just want to have a Ecobee smart thermostat to replace my existing thermostat. The installer never connected the C wire to the furnace or thermostat when 9t was installed (in 2022, new house). When I connect the blue wire from the thermostat to the C terminal on the control board and to the thermostat and start my system (removing the battery from the thermostat, the heat does not kick in (furnace is idle). As soon as I remove the blue wire and put the batteries in the thermostat, everything is fine. That's why I am confused. Thanks
It is possible that there is a problem with either the wire or the existing thermostat. Did you try hooking up the Ecobee? One thing to note is the R wire has to connect to the RC terminal on the Ecobee in order to power up.
If you're able to post a picture of the thermostat and furnace connections, that could help.
It does sound like you've done things correctly though.
Thanks again for the reply. I do not have the Ecobee yet (should get it in a few days). I have disconnected the C for now and will wait for the Ecobee to try it again. Will get back to you once I get it.
Thanks
Update. I tried it again with the old thermostat and checked with a multimeter at every stage. Works well now. I wired the same way as I said earlier so I don't know why it was not working. Should get my Ecobee in a few days so it should be all good. Thanks for the tip about the RC terminal on the Ecobee.