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Nest Compatibility

Coogan44
Community Member
  • I have a two zone thermopride furnace. I am looking to replace the first zone thermostat with a nest third generation. It is currently controlled by a Honeywell. The wiring on the first zone thermostat is Y,W,G,O,B with an R,RC jumper. Will it work?20220811_170007.jpg
18 REPLIES 18

CoolingWizard
Silver Product Expert
Silver Product Expert

Ok, let us try to figure this out.  So you a red wire going to Rh with a jumper to Rc.  This is the incoming approximately 24 Volts AC power for the control system. The White wire goes to W and this is typically energized for  call for Heating. Your thermostat connects Rh to W to initialize a call for heat. The Yellow wire is connected the Y and is used to call for Cooling. Your thermostat connects Rc to Y to initiate the cooling.  The Green wire is connected to the G terminal and is for the indoor Blower Fan.  When you put the FAN switch in ON, the thermostat connects Rc or Rh to G and that turns the blower on.  When the FAN switch is in AUTO, a  call for heat or cool also initializes G.  
You have a Black wire on the O terminal and this typically when energized from R, causes the heat pump reversing valve to switch. By default some systems are cooling systems and others are heating systems. So, O when energized, will change the reversing valve from cooling to heating, or from heating to cooling.  
There is a blue wire on the B terminal and this is typically the COMMON for the Rh and Rc. Smart thermostats need the COMMON wire to power them and if not a available, batteries would be needed to power the thermostat and changed when low.  To verify this, use a volt ohm meter and set to AC Voltage and check R to B and see if you get around 24 Volts AC.  It can very from 18 VAC, to 27 VAC. 

Do you have a Heat Pump system? 

Ken, The AC Cooling Wizard

NestPro and HVAC company owner

Ken,
   Thanks for reaching out. I have a York H1CA060S06A Cooling Air Conditioner. I am not sure if I have a heat pump for the forced air. Here are the read outs I have for the wiring
 
Blue .2
Brown 26
Green 26
White 26
Yellow 0
 

CoolingWizard
Silver Product Expert
Silver Product Expert

You have a straight AC Cooling system, split with the condensing unit outdoors and the and evaporator air handler indoors.  The air handler has the heating system with it. This heating system will either be Electric Heat strips or Natural Gas Burners.  

Your electrical readings tell me that the Blue wire on terminal B is not connected to the control transformer.  So there is no straight COMMON wire.  We should have seen the Yellow with voltage but it did not, odd.  I am not sure why there is an brown wire on O that is connected in the air handler.  

Do you have easy access to the location where the indoor air handler is located?

NestPro and HVAC company owner

I do. I am also going to add some pictures of the control boards. One show the internal control board and the other the zone control board. The top left of the zone control board wiring matches the internal control baord and connects the two. The bottom left shows the wiring for the thermostat. The O wire is red on the control board and that ties into the brown O wire that is connected to the thermostat. Ill take another reading of the yellow wire. 

CoolingWizard
Silver Product Expert
Silver Product Expert

Ok, if you have a zone controlled system, you typically have multiple thermostats or a manufacturer proprietary control system.  If this is the case, the NEST Learning Thermostat 3rd Generation is not capable of controlling a zoned system.  I am sorry.  Now, if each Zoned area has a separate thermostat system, there may be a way.  Would need to get a better understanding of your current thermostat and how it is programmed. 

Thank You,

Ken, The Cooling Wizard 

NestPro and HVAC company owner

i currently have two thermostats. One main thermostat and the other thermostat only has the red white and green wires going to it. 

CoolingWizard
Silver Product Expert
Silver Product Expert

In the second thermostat, are the wires connected to R,W and G terminals? If so, this thermostat controls a heating system. 

NestPro and HVAC company owner

Yes. That is correct. 

Coogan44
Community Member

So does that mean the Nest will not work with my system?

CoolingWizard
Silver Product Expert
Silver Product Expert

The heating thermostat can be controlled with a Nest thermostat, your cooling thermostat if the zone controls are in that old thermostat, would not be possible with a Nest Thermostat. 

NestPro and HVAC company owner

Is it possible to wire the second zone directly from the control board so that each one is controlled separately like the heat currently is? if i were to do that i assume i could use two Nest thermostats to control each zone. Do you have any sense of why they would wire the AC to be control by one thermostat but the het by two?

CoolingWizard
Silver Product Expert
Silver Product Expert

The basic problem is that the Nest thermostat does not have software logic to work with the zone controller to open a zone or close it.  Maoist zone controllers are connected to an intelligent thermostat that can be programmed to activate a zone or communicate with the zone controller and the zone controller would then activate the zone motor or open/close.  

NestPro and HVAC company owner

Coogan44
Community Member

I ended up purchasing a smartzone 2x to update my control board. I believe the nest will now work once i setup the new board as each zone will be controlled separately. 

CoolingWizard
Silver Product Expert
Silver Product Expert

With that approach, the SmartZone 2X, you can support two separate zones using 2 thermostats. Typically a thermostat in each zone area.  Each thermostat would be wired to SmartZone 2X.  Using this approach, you could indeed use two Nest Learning Thermostats 3rd Generation thermostats.  

NestPro and HVAC company owner

Thank you. Yo have been extremely helpful. Ill post once I get it all installed. 

MelbaDT
Community Specialist
Community Specialist

Hey folks, 

 

We appreciate your responses and thanks for taking care of this thread, CoolingWizard.

 

Coogan44, glad to hear that you've for the answers you're looking for. Keep us posted once you're able to install your thermostat. 

 

Best, 

Melba

MelbaDT
Community Specialist
Community Specialist

Hey Coogan44, 

 

Checking back in — have you had the chance to install your thermostat already? If yes, how is it?

 

Best, 

Melba

Jake
Community Specialist
Community Specialist

Hey Coogan44, 


I wanted to check in with you, and ensure you are good to go. Please let me know if you are still having trouble, as I will be locking the thread in 24 hours due to inactivity.

Best regards,
Jake