2023-07 Nest Gen1 and Honeywell K wire from a HVAC using a wire saver Honeywell THP9045A 1023

[Cparias]

I have an HVAC Lenox (Furnace and AC from around 2014). When this was installed, a wire saver box was also installed at the furnace which converts the HVAC 5 wires labeled as Rc, Y, G, C, W-O/B to Rc, K, C, W-O/B. So these are the 4 wires that go from the basement to the thermostat upstairs, a Honeywell (HW) Pro4000. The wire contacts at the Thermostat are Rc, Y, C, W-OB (Rc is bridged to R with a jumper). So the K terminal from the wire saver is mapped to the Y terminal at the Thermostat. This has worked for more than 8 years controlling AC, Heater, Fan.

I Installed the Nest Gen 1 thermostat connecting the wires as they were in the HW Thermostat (No jumper needed any more per Nest Instructions). Google Home App completes the setup, but I get E294 (No R Wire detected). Reset to factory and reinstalled multiple times ( at least 5 times). I can navigate on the Nest display, but it simply does not control the HVAC. In Home App went to wiring and noticed all wires are "Empty" as if it did not detect them. Googled that. Ok.. Checked wires are straight, gauge 18, 1/2 exposed. At the Nest connector board I checked Voltage between R-C, R-W, R-Y are all between 26 and 28Volts AC. Reset and reinstalled once more. Same results; E294 on display and App shows all wires "Empty", with no option to add those wires via the App.

@Hopeful opened a similar case back in 2022   (Search "2022 Nest Gen1 and Honeywell K") where a community user suggested it was safe to connect the K wire from the wire saver to Y at the Nest connector board, which is what I have done.

At this point my questions are:

1- Is the Nest Gen 1 Compatible with the Honeywell THP9045A 1023 wire saver?

2- If Yes, why would the Nest Therm not recognize any of the wires, other than cable straight, gauge 18 and wire exposed length. Is it defective?

Looks like@Hopeful resolved his problem by using the original 5 wires from the HVAC. If @Hopeful is still active, can you please confirm you bypassed the Wire Saver (seems like the same I have)? Had  you also gotten an E294 error when you tried to install the Nest Therm? Did you also get All wires Empty on the App? Was it a Nest Gen 1? 

Google support has said I need a Pro to do the install. I should not need to hire a Pro to tell me if that device is compatible or that it is defective, for a product that is claimed to  need 30 minutes to replace most thermostats. The Lenox HVAC is not a an antique and that wire saver is pretty common.

I would appreciate responses from the users who have some experience with this type of wire saver/ thermostat.

Thanks 

HW Pro40004 Wires5 to 4 wire boxNest Gen 1 BoardAfter Nest Gen 1 Install

[zoeuvre]

Hi Cparias,

Yikes! I'm sorry to hear the inconvenience you're experiencing with your Nest Thermostat 2020. Let's address your questions:

1. Your thermostat wires are compatible with the Nest Thermostat 2020 that you have right now and the wires should goes to the Nest Thermostat 2020's base as W wire to W terminal on the Nest Thermostat, Y wire to Y terminal on the Nest Thermostat, C wire to the C terminal on the Nest Thermostat, and RC wire to the R terminal on the Nest Thermostat, disregarding the jumper wire.
2. If the thermostat wires aren't configured properly in the Google Home app, it shows an error code. If a code doesn’t appear, the thermostat display shows the link to a wire setup guide. For example, if it shows https://goo.gle/3Ts62Me, you need to check the R wire. In this case, you must reset your thermostat to factory defaults and add your thermostat back to the Google Home app. If the issue persists, you must make sure that the wires are seated in the right terminals. Use the wire setup diagram of the app to move the wires to the right terminals. If there’s no wire setup diagram, refer to the picture of the thermostat wires before the installation. If there’s no photo, you can follow these instructions to access the system’s control board and take a picture of the wires. Use the picture to input the wires into the Google Home app.

Let us know how it goes.

Best,

Zoe

[Cparias]

Hi Zoeuvre,

I appreciate your taking the time to look into my issue.

Please review what I posted above. You will notice that I have already done what you have suggested, like 5 times: Reset the Nest, remove from the Home App, re-install, reconnect/verify wires, etc.

I need to know if Google Nest Gen 1 thermostat is compatible with the wires coming from the Honeywell THP9045A wire saver, because the Nest Therm does not seem to recognize them at all (R or any of the wires) as all of them show "Empty" in the app, even if they are straight, gauge 18 and expose 1/2", and have the right Voltage.

If it is supposed to be compatible, then the only choice appears to be that the Nest Thermostat is defective.

There must be some documentation as to whether Google does or does not work with this wire saver (or any other) or whether Google recommends to simply bypass it all together, which might be Ok if that is the case.

Someone may have suggested to use the Google power connector, but It seems to be needed if my system did not have a C wire, which I have. I just need Google to confirm. I should not need to hire an OnTech technician, which by the way, are not available in my area until the end of January 2024, to tell me this.

Thanks again.

[zoeuvre]

Hi there, 

The first-generation Google Nest Thermostat may not work with the Honeywell THP9045A wire saver due to its specific wiring configurations. Additional devices, like wire savers or adapters, can introduce compatibility issues. If you already have a C wire connected to your Nest Thermostat, using the Nest Power Connector should not be necessary as the C wire provides a continuous power source. Since we've already performed the necessary steps in addressing this issue, yet the thermostat still does not recognize the R wire, I highly suggest you return your Nest Thermostat 2020 to the store where you bought it in exchange for a new one and let us know how it goes.

Thanks,

Zoe