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Nest wiring with two red wires

Marco1955
Community Member

I’m installing a Nest Thermostat for my HVAC system. I have two red wires coming from the system. One is connected to R(heat) and the other RC(cooling) on the old thermostat. The Nest thermostat only has a connection for R . How do I connect  the RC wire. Thanks 

2 ACCEPTED SOLUTIONS

laurentbourg
Bronze Product Expert
Bronze Product Expert

I assume you have a Nest E or a Nest 2020 thermostat, those only have one R, previous versions of Nest thermostats used to show Rc and Rh separately. If you have a different system for your heat and cooling (for example, forced air for cooling and radiator for heating), you will need to get a Nest thermostat 3rd generation, the thermostat you currently have won’t work. If it’s the same system, then you can just use either Rc or Rh wires because they most likely come from the same transformer and put electric tape on the one you don’t use.  

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laurentbourg
Bronze Product Expert
Bronze Product Expert

The nest learning thermostats 1st gen/2nd gen/3rd gen will work. See enclosed link for all available types of nest thermostats. https://support.google.com/googlenest/answer/9246551?hl=en

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10 REPLIES 10

laurentbourg
Bronze Product Expert
Bronze Product Expert

I assume you have a Nest E or a Nest 2020 thermostat, those only have one R, previous versions of Nest thermostats used to show Rc and Rh separately. If you have a different system for your heat and cooling (for example, forced air for cooling and radiator for heating), you will need to get a Nest thermostat 3rd generation, the thermostat you currently have won’t work. If it’s the same system, then you can just use either Rc or Rh wires because they most likely come from the same transformer and put electric tape on the one you don’t use.  

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Thanks for the quick response. I looked at the wiring plate for the Nest Learning thermostat and that shows a R and RC terminal so I assume that would work too correct ? It’s cheaper than the 3rd generation 

laurentbourg
Bronze Product Expert
Bronze Product Expert

Which Nest thermostat model do you currently have?

I have a Nest thermostat  1.4 Only has R terminal 

laurentbourg
Bronze Product Expert
Bronze Product Expert

Ok that is the one with the mirror faceplate, it’s also called Nest wifi or Nest 2020. You cannot use that one if you have 2 different furnaces for cooling and heating. Do you have 2 different systems?

Yes that’s the one. Yeah I have a separate gas boiler and electric A/C unit with air handler unit which I assume is the reason for the two R wires. 

laurentbourg
Bronze Product Expert
Bronze Product Expert

Yes correct, there are 2 independent transformers so 2 R wires are needed. I do not believe there is a way around it, you will need either Nest 2nd or 3rd generation to solve this. 

Marco1955
Community Member

Last question. Will the Nest Learning work as well as the 2nd or 3rd gens?

laurentbourg
Bronze Product Expert
Bronze Product Expert

The nest learning thermostats 1st gen/2nd gen/3rd gen will work. See enclosed link for all available types of nest thermostats. https://support.google.com/googlenest/answer/9246551?hl=en

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Thanks very much for your help.