Incompatible thermostat wiring for Nest 4th Gen

[Ramina]

Hi, I am trying to replace my current A/C heating thermostat with a Nest 4th Gen one. In the App I was told that my wiring system is incompatible without any further explanation. I am curious if there is a fix. Here are the wires I have:

G, RC, RH, W/B and Y/0 - Simple A/c and gas-fired heater.

Any ideas are most welcome. Thank you.

[moralesvicente]

Hello @Ramina, 

Thanks for reaching out to the Google Nest Community Forum. I understand that you are trying to replace your current A/C heating thermostat with a Nest Learning Thermostat (4th gen); however, the Google Home app has indicated that your wiring may not be compatible. Don't worry; I'm here to help.

• To provide you with the most accurate information, could you please share a picture of your current thermostat wiring system? 

If you have any additional details, don’t hesitate to share them with me. 

Best regards, 

Daniel

[Ramina]

Many thanks for responding, Daniel. Look forward to hearing from you.

 

[moralesvicente]

Hello @Ramina, 

Thank you for getting back to me and sharing the requested information. Regarding your concern, your wiring system is compatible with the Nest Learning Thermostat (4th gen). I want to make sure everything is connected correctly for optimal performance, so please follow the diagram below.

• Green to G
• Red to RC
• Red to RH
• White to W1
• Yellow to Y1

For more information on how to install it, please refer to this article: Get started with your Nest Thermostat and Nest Learning Thermostat (4th gen).

If you have more questions, please feel free to let me know.

Regards, 

Daniel

[Ramina]

Thank you. What's the difference between Y1 and Y2?

[moralesvicente]

Hey @Ramina, 

Thanks for consulting more information; you can find the relevant details below:

• Y1 Wire: In most systems, the Y or Y1 wire controls your cooling system. If you have a heat pump, your Y or Y1 wire controls the compressor. Your compressor is responsible for both heating and cooling your home.
• Y2 Wire: This wire controls the second stage of cooling in conventional systems, which can help cool your home faster. In heat pump systems, the Y2 wire controls the second stage of your compressor, which helps heat or cool your home faster.

Don’t hesitate to reply to this post if you have any further questions. 

Regards, 

Daniel

[Ramina]

Thank you Daniel,

I have another question. I have a simple Nest thermostat with a mirror face. I want to replace a heating thermostat that only has a white and a red wires. The Nest has two batteries. Can I install the Nest without a C wire? 

Many thanks.

Ramin

[moralesvicente]

Hey @Ramina, 

Thank you for posting again! I understand you have a Nest Thermostat, and you want to replace a heating thermostat that only has two wires (red and white), and you’d like to know if this device is compatible to use without a C wire. It’s a pleasure to share more information. 

The Nest thermostat is designed for low power consumption, typically drawing sufficient power directly from the heating system. But, certain HVAC systems or voltage requirements may necessitate a common wire (C wire) or a Nest Power Connector for compatibility. The Google Home app automatically conducts a power test during the initial setup to determine and inform the user if a C wire is required for their specific system.

However, in this case with this type of thermostat, I recommend you connect a C wire or Nest Power Connector to ensure proper functioning.

If you have more questions, please feel free to write in this post.

Cheers, 

Daniel