1

I have a Nest Learning Thermostat (3rd generation) controlling the one zone of heating in my house and one zone of air conditioning, with red (Rh)/white (W1) wires coming from the boiler system and red (Rc), yellow (Y - cooling), green (G - fan), blue (C), orange (disconnected), black (disconnected), and white (disconnected) wires coming from the air handler for the air conditioning system. This thermostat has its blue wire inserted into its C port, but it reported that it was getting no power from the C-Wire.

1 Answer 1

3

Turns out I had blown the 3-amp fuse in the air handler when installing the thermostat (I crossed some wires).

In case it helps someone in the future, the printed figure at the top is a 3 to indicate its amperage rating, not an "E" like I first thought :).

3-amp fuse

3
  • 1
    For future readers - this is why its important to turn off power to your HVAC before working on the thermostat wiring. The thermostat voltage is low enough that it won't shock you so many people don't turn off the power, but one slip of a wire or screwdriver will hopefully cause a blown fuse that you now have to locate and replace. Worst case, the fuse doesn't blow and the control board is damaged.
    – JPhi1618
    Commented May 6, 2022 at 15:13
  • 1
    And don't just trust your circuit breaker! I had turned off all circuits labeled "A/C" and "furnace" and anything else that looked similar, but that air handler was on a different circuit I guess. There was a switch on the unit that turned off power to it. I should have checked that first (but it was in the attic and there were snake skins nearby and I was a chicken)! Commented May 6, 2022 at 15:17
  • 1
    Good point, those breakers should have cut power to the thermostat, but sometimes the 24v section of the furnace ends up getting wired into a general lighting circuit nearby. A switch in the attic should always be provided as a "service disconnect" per code, so at least you do have that.
    – JPhi1618
    Commented May 6, 2022 at 15:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.