r/Nest • u/NYSports1985 • 4d ago

Google recommended wiring issue

Gallery image

Gallery image

Gallery image

Trying to install third Gen Nest thermostat. I contacted Google after the app said my existing wiring needs their assistance. After following their instructions, I turned on my ac/furnace and it turned on, then immediately turned off. It did this a couple more times before I was able to get to my panel to shut down my furnace and prevent any damage. Pictured is my existing wiring, as well as the instructions from Google on how to wire the nest.

I have oil heat, forced air, with one AC condenser. Upstairs is controlled by slave thermostat (currently nest 3rd gen as well). This attempt to install was on my first floor thermostat.

Any idea if I can hook up a nest or am I stuck?

0 Upvotes

50% Upvoted

13 comments sorted by

View all comments

2

u/ebusch73 4d ago edited 4d ago

Yeah, that's not correct. In some cases (like Trane) the B wire is the common, but in your case it looks like your B is actually B (reverses cool to heat) and you also have an O wire (reverses from heat to cool). Most heat pumps use a single wire for O/B, and it configured as one or the other. I don't think Nest supports heat pumps that need individual O and B wires.

1

u/NYSports1985 4d ago

Okay. I’m surprised Google told me, on two occasions, that my wiring would work. There is an additional wire in the wall, as well as one at the panel on the furnace with an open C terminal, but anytime I put a C wire as an option on nest app it says it won’t work anyway.

1

u/ebusch73 4d ago

I think you'd likely need some help from an HVAC tech to see if its possible to reconfigure your system to work with a single OB wire, but that may be an expensive operation as it would likely require a replacement changeover valve.

1

u/NYSports1985 4d ago

Thanks. I might just stick with a dumb thermostat if that’s the case. Appreciate your input