Nest Thermostat - "Rc" wire has nowhere to connect

[jdvaughn04]

I have a google nest thermostat that I'm trying to install. My old thermostat has an "R" and an "Rc" wire. The Nest thermostat only has an "R" terminal. Where do I connect the "Rc" wire?

For reference - my old thermostat had wires connected to G,W,Y,R and Rc.  The Nest thermostat has terminals for Y,C,W,G,R and *OB.  All of the wires from my previous thermostat have a place to connect to on the Nest thermostat except for the Rc wire.  Please advise.

[CoolingWizard]

@jdvaughn04 , if your current thermostat has both a thermostat conducting wire attached to RC and a thermostat conducting wire attached to R, then this would indicate that you have two separate systems one for heating and one for cooling. In this particular case you will be required to purchase a Nest learning thermostat. To verify this means that you have a separate, probably hot water boiler for heating, and a separate air conditioner system for cooling. And you do not have an integrated air handler furnace/air conditioner .

AC Cooling Wizard

[jdvaughn04]

CoolingWizard you summarized it perfectly. But I don't have a C wire so I don't think I can use the learning thermostat either, right?

[CoolingWizard]

@jdvaughn04 , this depends on the HVAC equipment.  The Nest Learning Thermostat has the ability to use an alternate path to reach the Power Common.  This is when the air conditioner is on the Nest uses the W wire to reach the Common Power,  and when the heating is on the Nest uses the Y wire to reach the Power Common.  
However, if the system is a more modern system with a digital control system this alternate path to reach common most likely not work.   Are there any unused wires of your thermostat cable?

AC Cooling Wizard

[jdvaughn04]

Thanks again for the reply.  I don't see any unused wires at the location of the thermostat.  I have a G,W,Y,R and Rc that are all connected to the current thermostat.  If I bought the "Nest Power Connector" w/ the Nest Learning Thermostat, do you think that would work?  Would I need to install it at the A/C in the attic or the furnace in the basement?  Thanks!

[CoolingWizard]

@jdvaughn04 , can you tell me about your HVAC system? They provide your heating and your cooling. Because you have an R wire and an RC wire, lead me to believe that you have a separate heating system that is not part of the air-conditioning cooling system.

AC Cooling Wizard 

[jdvaughn04]

CoolingWizard - that is correct.  I have a furnace that provides hot water to baseboard heaters for my heat.  That system has 2 zones on it so I have 2 thermostats total in the house.  I also have a Carrier cooling unit in the attic w/ the condensing unit on a pad outside of the home.  That system only has 1 zone.  I currently have a Honeywell programmable thermostat that controls the 2nd zone of the heating system.  I also have a separate Honeywell programmable thermostat that controls the 1st zone of the heating system, as well as, the cooling for the entire home (1 zone only).  This thermostat (the one with heating and cooling) is the one I'm trying to replace with a smart thermostat.

[CoolingWizard]

This can still work using the Nest Power Connector.  To confirm you do not have an unused conductor wire in your thermostat cable.  Sometimes the installers leave them tucked inside the wall. 

AC Cooling Wizard