Nest Thermostat wiring

[Fawnsee]

I have an old Honeywell T8085 thermostat that I am replacing with a nest. I have opened it up but the wiring is confusing me. The red cable goes to three separate points. It starts at RH then goes to RC and finally ends at C. Should I just install it on RH in the nest and Ignore RC and C? 

[Fawnsee]

Here is a picture of the original wiring. 

 

[DaveLister · Accepted solution]

Nest thermostats have an internal jumper between Rh and Rc that it will utilize if necessary (https://support.google.com/googlenest/answer/9250973). Put the red wire into either one of those two terminals on your Nest. Based on Fig. 7 at https://www.manualslib.com/manual/730027/Honeywell-Q682b.html?page=4 and the discussion at https://www.googlenestcommunity.com/t5/Nest-Thermostats/Two-C-Wires/td-p/305935, check that the wire on the other C terminal is connected to the C screw on your HVAC system. If so, put that wire into the C terminal of the Nest. Otherwise, you'd probably want to contact a professional for assistance.

[Fawnsee]

I ended up wiring the red cable to Rh and just ignoring the Rc terminal and the other C terminal. Everything is working fine on the device. 

[DaveLister]

Glad to hear it. Don't forget to put a cap on the wire that was attached to the C terminal, just to be on the safe side.

[zoeuvre]

Hi Fawnsee, 

I'm glad that everything has been covered here. 

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. 

Thanks for your help, @DaveLister.

All the best,

Zoe