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Old 12-11-2022, 10:54 PM   #1
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Join Date: Apr 2019
City & State: Deshler,Ohio
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Default Nest Thermostat Discussion...


I was over my sons place helping him with projects today. (Broken Dryer Belt, a Couple leaking pipes (One cracked - that got me over there),and Thermostat swap.

The Energy company offered a Rebate on the Nest Thermostat System (Not the Learning One) last year and we picked it up and its sat in the shipped box for about a year now.

Anyways I was thinking it would be a quick job as I currently have a Nest Learning Thermostat at my place and it was not a problem to install. (Old Rheem 90 Furnace)

At my boy's place he has a York Stellar Furnace (120K) (Natural Gas Forced Air) put in by my late father and I back in 2001 replacing a Old Gravity Fed Coal converted to LP Gas Furnace. That job was a decent task as most of the duct work on this two story home was replace/deprecated/adapted. House was built in 1882. There is no Central Air Conditioning or other Heating and Cooling Devices in the Home. The Thermostat Wiring is Solid Core Thermostat Wire I am not sure of AWG but it was sold as Thermostat Wiring at that Time. It is quite literally a straight drop to the furnace say maybe 12 ft of wire between floors including organized neat connections.

The Furance Connections (at Furnace) consist of 4 Terminals (Red, Green, Yellow, White). Yellow is not Connected (Think Y Extra wire not used Scenario)

The Old Themostat, a Programmable From Honeywell,.I believe I put in the place back in 2005. Replacing another Honeywell that we put in 2001. The 2005 one had more programmable options so I added it. The late Honeywell Thermostat Utilized 3 of the 4 wires (RC, Green, White).

This previous Thermostat to the Nest also used a Jumper from RC to RH (came in place with thermostat originally).

So Basically the way I understand things, Please correct me if I am wrong, is the Red Wire is 24 Volts DC. The White is for Heat. The Green is for Fan Blower. If the Yellow was involved it would be for the Central Air.

If there was a C wire its a Common 24 Volts Continual. (For Items such as the Nest Thermostat charging etc).

So In the Nest (Phone app) setup it pushes (Forces) the user to Buy their Nest Thermostat C Wire Adapter.

This Actual Nest C Wire Adapter appears to be nothing more than a box with connectors while many other competitors are using a 24 DC Transformer which just replaces the C Wire. The Competitors boxes can be for more than just Thermostats.

If during the Setup you say that you have this Adapter it will let you progress thru the steps and the Thermostat/the furnace seems to function fine. If you do not say you have the adapter it tells you its incompatible. I temporary said I did have the Adapter as I had already mounted the optional back thermostat mount plate and the base plate to the wall and proceeded to completion.

The thermostat does display N260 Error on occastion which means no Common Wire Detected.

My question I guess is the Common Wire is also a 24 Volt source, the way I understand things. Why not just split (Jumper) the Red Wire to the Common Connection on the Thermostat? This would create a parallel connection of 24 Volts.

It appears that the Nest C Wire Adapter is doing something similar as there is no additional transformer.

The only thing I can think of is the Amperage may not be there but many of the 24 Volt Non Google /Nest Adapters are only .2 amps to a max I have seen of .5 amp at 24 Volts. The .5 amp one handles more than The Nest Thermostat (EcoBee and Honeywell) as well as other Household 24 volt needs.

Unfortunately this is not something you can get a confirmation on from Google/Nest. Not to mention I would also assume it would be different from furance to furnace (24 Transformer capability/setup).

The Adapater probably has a few diodes etc for protection I bet.

Thoughts, Anyone try something similar?

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