Showing results for 
Search instead for 
Did you mean: 

Replacing a 25 year old thermostat

Community Member

Replacing two thermostats on a zoned system.  The first one worked fine--it had Y, W, R, G and (aside form needing a Nest Connector) set up relatively easily.  Second thermo had Y,W,RH bridge to RC and G, plus an extra white and an extra yellow connected to the back of the board. (not sure if that's relevant).  On the Zone Controller, though, the green wire is not connected.  It was stripped, but wrapped around the shielded cable behind the controller.  Of course, Nest can's see it.  My question is, do I simply connect the green wire to the ZC?  Or should I call a Pro?



Platinum Product Expert
Platinum Product Expert

Post a picture of the original thermostat's wiring and of the zone controller wiring with its manufacture and model information.

Zone controllers can be finicky at times.

old thermo wiringold thermo wiringback of old thermo boardback of old thermo boardZC  thermo sideZC thermo sideZC equip sideZC equip side

Also, ZC is Carrier ZONECC3ZAC01 operating two systems with AC and Gas heat with a damper system.

Finally, I purchased Nest Controllers since C-wires were not connected on old thermostats.  However, the wires are there, just wrapped around the cable.  Can I simply connect them at each end instead of using the Nest Controllers?

Community Specialist
Community Specialist

Hey folks,


Thanks for visiting the Google Nest Community. 


Since this thread hasn't had activity in a while, we're going to close it to keep content fresh.

If you have additional questions, feel free to submit another post and provide as many details as possible so that others can lend a hand. 


Hope this helps!


Kind regards,