Replacing Honeywell R/G/Y/W thermostat with Nest

[idickers]

I'm replacing a Honeywell RTH7600 thermostat with a Nest Learning thermostat.  The Honeywell only uses 4 wires, Red, Green, Yellow, White.  The Nest requires either Rc or Rh.  I'm not sure which one the Red wire on my Honeywell corresponds to.  My only clue is that there is an Rc port on my Honeywell thermostat that is unused.

Can I assume that the R wire on the Honeywell corresponds to the Rh on the Nest?

Thanks for any help!

[CoolingWizard]

Your safest bet is to follow the installation instructions, precisely as given, and then place the red wire on RC of the nest backplate. Yellow on Y or Y1, White wire on W or W1, and green wire on G.  It sounds like you have a conventional air conditioner with a gas furnace or perhaps a oil fired furnace.

Ken, The AC Cooling Wizard

[idickers]

Thanks for the suggestion.  Where is this listed, I couldn't find any directions for what to do if the existing thermostat only has a Red wire, not Rc or Rh.  I connected the red wire to Rh since Rc was unused on the old thermostat, and it seems to be working although the battery is low and does not appear to be charging.  

Does this suggests that Rc might be power and I haven't made that connection?  I can swap the Red wire from Rh to Rc and test.

[CoolingWizard]

Here are some basics about the HVAC system controls.  The thermostat is what action is needed by determine monitoring the system mode setting and the temperature set point.  If you system is in heating mode, it looks for the temperature to fall below the set point and generates a call for heating.  Now, how does the thermostat do that? It connects the R terminal to the W terminal.  Since the R terminal is the input power, this power is connected by the thermostat to the W terminal. This power travels to the furnace control board and that invites the heating cycle.  Likewise when in cooling mode the thermostat monitors the temperature and it rises above the set point, the thermostat initiates call for cooling.  It does this by connecting R to Y. This power passing down the wire attached to Y connect to the indoor air handler and onto the outdoor compressor. 

When you install a Nest thermostat, the thermostat asks you to install the Nest App, and the nest app connects to the thermostat and initiates the configuration process.  Before that of course, you mount the baseplate, connect the wires. When snap the display to the baseplate the installation process begins .

I hope this helps,

Ken, The AC Cooling Wizard 

[idickers]

Thanks, that is a very concise explanation, and I appreciate your help!

To my original question, if my old system only has a Red wire, do I connect it to Rc or Rh of the Nest Thermostat?  

[CoolingWizard]

Just connect the red wire to the arc of the Nest backplate. 

The AC Cooling Wizard

[idickers]

Will do!  I assume you meant Rc?  Thanks so much for your help!

[CoolingWizard]

Sorry, autocorrect got me, yes RC.

The AC Cooling Wizard

[Markjosephp]

Hello folks,

I wanted to ensure that everything was covered here.

Thanks for the input, @CoolingWizard.

@idickers, I wanted to see if you were able to install your new Nest Thermostat successfully. Please let us know if you have any other questions or concerns.

Regards,

Mark

[idickers]

Thanks, got the Nest Thermostat installed and it works like a champ!

[Markjosephp]

Hi idickers,

Awesome! I'm glad to hear it's up and running. It looks like we can consider this one complete, so I will lock the thread within 24 hours unless I can help out with anything else.

Regards,

Mark