Dual Zone - Heat Pump Advice

[Jimsngc]

Hi,

Just bought a house with an existing "dumb" thermostat HVAC build.

I have a dual zone HVAC unit with heat pump.  I just purchased 3x "Google Nest Thermostat - Smart Thermostat for Home - Programmable Wifi Thermostat - Snow" which I assume are the "E" type but not 100% sure.  The existing dual-zone thermostats have the following connectors, all with wires: C, W(/E), O/B, Y, R, G.  I am seeing conflicting advice on whether to enable the "heat pump / dual-heat source" when I set these up.   The existing thermostats for the dual zones do not have an Emergency Heat setting whereas the 3rd thermostat for the non-zoned unit upstairs does.  Some sources say the zone controller board will handle the heat pump/dual-heat source setting as needed but the presence of O/B cable seems to indicate this is not the case (or so I read anyway).   

I would appreciate anyone with more experience who might have some knowledge to share?

The HVAC system is an American Standard (Silver): 4A6H6024H1000AD

Thanks in advance.
(Please note that the issue with Zone3 being the "in" and Zone2 being the "out" in the image below has already been fixed.   Must have been a Friday afternoon when whoever installed this did the wiring).

Zone Control BoardGR C O/B W Y

[AndersC · Accepted solution]

Hi @Jimsngc,

Thank you for reaching out to the community. I understand you are seeking guidance on the correct configuration, specifically regarding the "heat pump / dual-heat source" setting, when installing your new Google Nest Thermostats with your existing dual-zone HVAC system and wiring. I'm here to provide you the information requested.

It appears you have the Nest Thermostats (2020) model. Based on the wires you mentioned from your existing thermostat (C, W(/E), O/B, Y, R, G), your Google Nest Thermostats (2020) are compatible with your dual-zone heat pump system.

The standard wires you listed correspond to the following functions, which the Nest Thermostats can handle:

• G (or G1): Fan

• Y (or Y1): Cooling/Heat Pump Compressor

• W (or W1): Auxiliary/Emergency Heat (or second stage heating)

• R: Power (Heating or Cooling)

• O/B: Heat Pump Reversing Valve

• C: Common wire (provides constant power, required for the Nest Thermostat (2020) in some setups like zoned systems).

Here are the step-by-step instructions for the setup in the Google Home app:

1. Preparation: Before removing your old thermostats, ensure you turn off the power to your HVAC system at the breaker to avoid damage. Take a photo of your old thermostats wiring for reference.

2. Physical Installation: Install the Nest Thermostat bases and connect your existing wires to the appropriate terminals on the Nest bases.

   • Connect the G wire to the G terminal.

   • Connect the Y wire to the Y1 terminal.

   • Connect the W(/E) wire to the W1 or * terminal (the app will guide you on how to configure this for Auxiliary/Emergency Heat during software setup).

   • Connect the R wire to the Rh or Rc terminal (or the single R terminal if present).

   • Connect the O/B wire to the O/B terminal.

   • Connect the C wire to the C terminal.

3. App Setup: After the devices are physically installed and you've restored power, open the Google Home app to complete the setup.

   • The app will prompt you to enter the wires you connected. Accurately select the terminals you used (G, Y1, W1, R, O/B, C).

   • The app will use this wiring information to automatically detect that you have a heat pump system.

   • Follow the remaining in-app steps to finalize your system configuration, including setting the reversing valve position (O or B) if prompted, which is crucial for heat pump operation.

The Google Home app is designed to guide you through this process and configure the more complex heat pump and auxiliary heat settings (often handled through the W1 terminal) to ensure your system runs correctly.

If you encounter any difficulty or the app advises that your system is incompatible, it is generally due to the multi-zone setup requiring a constant C wire connection for power, which it appears you already have.

Keep me posted. I'll be waiting for your response.

Regards,

Anders

[Jimsngc]

Thank you so much for taking the time to provide such a detailed response!   It is very much appreciated.

I plan to tackle this install over the weekend and will report back how it goes.

Jim

[Jimsngc]

Hi Anders,

All 3x installed and as far as I can tell working as expected.   
Thanks again for the help.
Jim