Nest Learning Thermostat Wiring Standalone Use

[MidwestVince]

Hello: I have been using my Nest Learning Thermostat and Nest temperature sensor for a few years with my Heat Pump/Gas Furnace + Humidifier setup. 

I've totally replaced my HVAC system with a new Trane 2 stage modulating AC and Gas Furnace, which required the use of a Trane thermostat (Nest Learning Thermostat not compatible).  

Can I use the Nest  thermostat just as a standalone temperature/humidity sensor and power it with a 24vac power supply?

If so, what connectors on the wall plate should I connect the power supply to to just power up the thermostat?

I would connect it to my wifi to pull up local weather, and pair it with the remote temp sensor to get readings from other rooms in the house.

Has anyone else done this, or did you just get rid of the Nest thermostat altogether since it wasn't compatible?

Thanks,

Vince 

[EdmondB · Accepted solution]

Hi there,

As long as there are two wires connected on the Nest thermostat base with at least 16 to 24 volts, that should work. You can just connect the two wires on W1 and RC/RH as a fake heating system using the wires coming from the 24 volt power supply. Once it recognizes the wires on the W1 and RH, you can just use that as a standalone thermometer.

Let me know if you have additional questions.

Regards,

Edmond

[CoolingWizard]

@MidwestVince , The Trane you have has a model number on the outdoor unit.  Can you please get me that model number ?

AC Cooling Wizard

[RightStuff]

I don't even know if the AC is a Trane. It's on the roof of a 2 story 4 plex. Will need to rent a ladder. Is there another solution to this problem above?

[CoolingWizard]

@RightStuff , I am sorry this, message thread was started by @MidwestVince , if you have away questions you should create your own message thread so we can help you. 

AC Cooling Wizard 

[CoolingWizard]

@MidwestVince , your contractor that installed your new Trane system should have given you an owners manual with the model number written in it by the contractor.  This is information is needed in order for you to register online for the extra 5-year warranty, unless of course, you live in California.  

AC Cooling Wizard

[MidwestVince]

The Furnace is a XC-95M, and the AC is an XV20i.

I am registering everything for the extended warranty.

Since the new system is not compatible with the nest learning thermostat, I was just wondering if I could power up the Nest Thermostat with a 24vac power adapter only, connect it to wifi, and use it as a standalone thermometer and weather display.

Thanks,

Vince

[CoolingWizard]

@MidwestVince , Thank you for responding. Those are the general equipment class, the actual model number is on the label on the outdoor unit and on the label of the indoor unit. You outdoor heat pump will have a model number like 4TWV0X48A. Your furnace will have a model number like TDHMD120BC.  Now here is the rub so to speak. Manufactures have been trying to find a way in order to help contractors to make more money and for the manufacturers to make even more money. How do they do this? They utilize a proprietary and digital communications interface using a 2-wire RS485 communication is protocol. The end result is you have to buy a very proprietary and very expensive thermostat to communicate with your indoor and outdoor units. Now, the manufactures do indeed provide a conventional interface as well and your system includes this.  The control board in your Furnace has the conventional W1, W2, G, R, Y1 and C. the communication to the outdoor unit will need to remain digital however. This will require your contractor to return and rewire and then reprogram the personality module of the furnace.  

AC Cooling Wizard

[Jenelyn_O]

Hi folks,

Thanks for reaching out. I just want to check if you managed to see the response above. Please let us know if you still have questions or concerns, as we'll be willing to assist you further. 

@RightStuff, please tell us more about your concern by creating your own thread. We would like to assist you from there.

I appreciate the help, @CoolingWizard.

Best,

Jenelyn

[MidwestVince]

I did see the responses above, but my original question was not answered.

In a nutshell, I have a new Trane Furnace and AC with it's own new thermostat. It uses proprietary wiring, and it is not, in fact, compatible with my Nest Learning Thermostat. The Trane thermostat links with the Trane App, and I can manage it all through my Google home app just fine.

I wanted to see if the Nest Learning Thermostat can just be powered up with a 24VAC power adapter, and used only to monitor the temperature, humidity, and display with weather.  I have a separate Nest temp sensor that I would pair with it and throw in another room. I just want to see if it's possible. If it's not, no big deal--I'll just reset and throw it on eBay.

[EdmondB · Accepted solution]

Hi there,

As long as there are two wires connected on the Nest thermostat base with at least 16 to 24 volts, that should work. You can just connect the two wires on W1 and RC/RH as a fake heating system using the wires coming from the 24 volt power supply. Once it recognizes the wires on the W1 and RH, you can just use that as a standalone thermometer.

Let me know if you have additional questions.

Regards,

Edmond

[EdmondB · Accepted solution]

Hey there,

Checking in to see if you still need help. Let me know if you have additional questions.

Best,
Edmond

[MidwestVince]

That worked, and thanks! I needed an AC adapter with at least 1 amp to activate the Nest.  A 24vac adapter with 300ma kicked it on, but it threw errors, and a more powerful adapter did the trick. Thank you! 

[EdmondB]

Hey there,

Awesome — glad to hear that, and thanks for getting back to us. If you have any new issues, updates, or just a discussion topic, feel free to start a new thread in the Community.

Best,
Edmond

[MidwestVince]

Thanks Edmond! I did start a new topic over in the cameras section yesterday regarding my bandwidth hogging Nest Indoor Cam! We'll see if I get a solution on that!

Vince

[EdmondB]

Hi there,

Got it. I’ll try to check the thread and see if I can add some input to it. Let me know if you have other questions.

Best,
Edmond