topic Re: Original nest thermostat flagged as not compatible in Nest Thermostats

Original nest thermostat flagged as not compatible

dashman — Thu, 19 Oct 2023 19:45:23 GMT

I've got a single stage heating and cooling system - 24V AC thermostat and solid wires.

These pins are wired on my current thermostat

W RH RC C G and Y

This is the original Nest thermostat - any help appreciated.

Has connectors C Y W G R *OB

Re: Original nest thermostat flagged as not compatible

CoolingWizard — Thu, 19 Oct 2023 20:26:49 GMT

@dashman , I am not sure why you feel your system is not compatible. Your old thermostat should have a jumper wire connecting Rc to Rh. I used the Nest Compatibility checker and your system is fully compatible with all of the Nest Thermostats.

AC Cooling Wizard

Re: Original nest thermostat flagged as not compatible

dashman — Thu, 19 Oct 2023 22:26:19 GMT

Isn't Rh to turn on heating and Rc to turn on cooling?

Anyway not jumped together right now??? But if I think hard I think years ago I did see a jumper but I don't remember which terminals.

Does it make sense to jump heat and cool modes together - just asking?

My thermostat is the white-rodgers unit and has a slide switch to toggle from COOL to OFF to HEAT.

This is the original thermostat and can I get a link to the compatibility tester.

I scanned the code on the unit with Google home app and it told me to specify the connected wires and then said not compatible.

Re: Original nest thermostat flagged as not compatible

CoolingWizard — Thu, 19 Oct 2023 22:47:29 GMT

@dashman , the Nest Thermostat has the ability to internally between Rc and Rh when needed. The R terminals are input power. When the heating system is 100% separate from the Cooling system. Then heating system would supply power to Rh and the separate cooling system would supply power to Rc. All thermostats have a system mode switch. The Nest has the system mode as well only it is a touch screen that allows you to select heat or cooling mode. Your wires are R, C, W, Y, G. The comparability checker can be found at: https://store.google.com/intl/en/widget/compatibility/thermostat/

If you choose the Nest Learning Thermostat the backplate will have Rc and Rh whereas the basic Nest Thermostat has only the R.

AC Cooling Wizard

Re: Original nest thermostat flagged as not compatible

dashman — Thu, 19 Oct 2023 22:58:53 GMT

In your first sentence - is that "internally SWITCH between".

The thermostat UI will let me switch between hot and cold. even though both Rh and Rc lines connected to R - that's ok?

You're right - your link compatibility checker prompts whether Rc and Rh is jumped - whereas the one in the app - just says NOT after I enter the wires on the old thermostat.

So I connect C, G, Y and W one to one and then connect both Rh and Rc wires to R on the new Google thermostat. Right?

My heat is gas boiler and cold is electric central A/C.

Re: Original nest thermostat flagged as not compatible

CoolingWizard — Fri, 20 Oct 2023 04:32:20 GMT

@dashman , do you have two separate wires one in Rc and separate wire in Rh? Not a jumper wire but two separate wires. You cannot put two wires in a single backplate terminal.

AC Cooling Wizard

Re: Original nest thermostat flagged as not compatible

dashman — Fri, 20 Oct 2023 00:26:53 GMT

Yes - there's two separate wires going into Rc and Rh.

I've got another thermostat downstairs for just heat (no A/C) and that has two wires coming out the

wall - one goes to W and another goes to Rc - and both Rc and Rh are jumped.

The same gas boiler heats both downstairs and upstairs. Uses natural gas.

The A/C system is electric - upstairs only.

Re: Original nest thermostat flagged as not compatible

CoolingWizard — Fri, 20 Oct 2023 02:17:35 GMT

@dashman , since you have two seperat systems, you will need a Nest Learning Thermostat. When the systems are separate, that is the gas furnace does not share a forced air handler with the air conditioner. So your boiler uses baseboard or radiators in the rooms.

ACCooling Wizard

Re: Original nest thermostat flagged as not compatible

Patrick_Caezza — Fri, 20 Oct 2023 02:56:24 GMT

@dashman

Post a picture of the original thermostat wiring

Re: Original nest thermostat flagged as not compatible

dashman — Fri, 20 Oct 2023 19:51:00 GMT

@Patrick_Caezza

@CoolingWizard

Here's the wiring of the old thermostat.

Heating is gas boiler and cooling is electric.

Thanks.

Old Thermostat Wiring

Re: Original nest thermostat flagged as not compatible

CoolingWizard — Fri, 20 Oct 2023 22:20:28 GMT

@dashman , you indeed require a Nest Learning Thermostat to support separate heating and cooling systems. It appears you have two separate black insulated conductors. One is attached to Power Common and the other one is attached to W. Make sure you keep them straight so as not to create a direct short.

AC Cooling Wizard

Re: Original nest thermostat flagged as not compatible

dashman — Sat, 21 Oct 2023 00:07:02 GMT

Thank you for your help - I appreciate it.