Nest Thermostat Terminals

[Pjwalters1592]

What are the terminal (Y, C, W, G, R, *OB) functions? I could not determine the wire colors on my old thermostat, but I have traced the wires back to the system control board and know their functions. I just need to know where I should connect them to the Nest. 

[CoolingWizard]

@Pjwalters1592 

I would be more than happy to explain. 
Y/Y1 is the Compressor Relay, Stage 1

C - is Power Common, 24 Vac if it helps, think of it as the Neutral

W - Stage 1 Heating, with Heat Pumps this is Auxiliary Heat

G - Blower Fan Relay

R - Power 24 Vac, think of this as the Line

*OB is the Heat Pump Change Over Valve. 
Check your  your air handler control board, see what color wires is on which of those terminals and match that same color wire on the same terminal letter on the nest thermostat.

AC Cooling Wizard

[Pjwalters1592]

I can’t get to the Nest until tomorrow, but I’ll let you know. I think you solved my problem. Thanks!

[Pjwalters1592]

 These are the connections in the heating a cooling system. The 4 wires from the thermostat are Red, Green, Orange (Y?), and White. Here are the connections at the Nest. 

 I have heat but no AC

[Jake]

Hey Pjwalters1592,

Thanks for the help CoolingWizard.

I wanted to check in and see if you managed to see CoolingWizard's post. Please let me know if you have any questions from here. I would be happy to assist, and make sure you are good to go.

Best regards,
Jake

[Pjwalters1592]

Hey, thanks for checking in. I found that the Y terminal in the nest itself is bad. I sent it back under warranty.  Thanks again!

[zoeuvre]

Hi there,
 

As we got our resolution here, I'm going to mark this thread as complete. I'll be locking this thread if we won't hear back from you again in 24 hours. Should that happen, feel free to create a new one if you have more questions or have other concerns in the future. 

All thanks for your help, @CoolingWizard and Jake. 
 

Cheers,

Zoe

[CoolingWizard]

The wiring looks correct. You need to check your system. Verify your wires are straight and are fully inserted. Go to SETTINGS > EQUIPMENT At this point, you will see a black plate and see what wires are being recognized.  Is Y recognized.