One of my two Nest Gen2 thermostats' fan doesn't run

[plutokov]

I had two Trane XB AC units, and two Nest Gen 2 thermostats installed with Venstar Add-a-Wire accessories (which are to convert 4 wires to 5 wires), because there are only 4 wires from the wall and Nest thermostat needs 5 wires to run the fan. Everything is working fine (iPhone scheduling cooling/heating, etc.), except one fan cannot be turned on. The Trane technicians even swapped the thermostats without any luck, so they gave up. After struggling for many years, I hired another pro to reinstall the Venstar add-a-wire accessory, and we got exactly the same problem. The pro thinks the thermostat base might have issues. The question is how do I know the thermostat base is deficient? Can you help? Thanks.

[GabrielaG]

Hi plutokov,

Thanks for reaching out to the community. I am sorry to hear that your thermostat is not turning on the fan, but no need to worry; help is here.

I'd like to ask you a few questions in order to gather more information about the concern and find the best way to fix it.

• When did the issue start?
• What other strange symptoms have you experienced since the problem started?
• Are there any error messages? If so, what are they exactly?
• Does the issue happen on heating only, cooling only, or both?
• Do you have a common ground wire or C wire?
• Have you checked the power readouts on the Nest thermostat? (settings> Technical info> Power: VOC, VIN,LAN Battery)

If you have any additional details or information that might be helpful, please feel free to share them with me.

Best regards,

Gabriela

[plutokov]

Hi Gabriela,

Sorry, I just saw your message. Here are my responses to your inquiries above.

• The problem started when I first installed the two nest thermostats several years ago; meaning it never worked for one thermostat.
• No; the function just doesn't work for one thermostat (the function of the other thermostat works just fine).
• No. I can see the fan icon turns on my iPhone and the thermostat when I manually turn on the fan function, but there are no air flows.
• When the AC is cooling or heating, the AC fan works fine and there are air flows in the room as normal. I just cannot manually or automatically turn on the fan when AC is not cooling or heating.
• I've attached the original wiring (before we installed the "Add-a-Wire" accessory).
• Please see the attached.

Thanks.

[GabrielaG]

Hi plutokov.

Thank you very much for keeping me updated and sharing the information with me. I'm sorry to hear that the difficulty is still not remedied. I see you provided me the previous wiring for your thermostat before installing the "Add-a-Wire" accessory. 

To get a better understanding of the situation, please help me out by answering the following questions:

• When was the "Add-a-Wire" accessory installed?
• Can you please send me a picture of your new waiting with wire accessory? 

Any additional details you can provide will be helpful.

Regards,

Gabriela

[plutokov]

Hi Gabriela,

Attached is the current "Add-a-Wire" wiring (the one working has the same wiring). I think the accessory was installed in 2019 (based on my notes) when I changed our AC units, and it had been installed and reinstalled for several times by several different pros because of the issues.

Thank you.

[GabrielaG]

Hi plutokov,

Thank you very much for sharing this information. I'm sorry to hear that the problem is still not resolved. I see the photo that was sent with the "Add-a-Wire" wiring diagram. Since only one of the two thermostats is having issues, I would recommend swapping the thermostat display with the one that is working to see if there is a problem with the thermostat backplate.

Let me know how things go.

Regards,

Gabriela

[plutokov]

Hi Gabriela,

I swapped the displays and it didn't resolve the issue. We think there is some issue with the backplate, but how do we verify that?

[GabrielaG]

Hi plutokov,

Thank you very much for sharing this information. I'm sorry to hear that the problem is still not resolved. I appreciate you performing these steps with me. I would recommend swapping the wires Y1 and G to see if there is a problem with the thermostat backplate. 

• Please check this in your HVAC when you perform the wire swap:
• If the compressor is running when you activate the heating?
• Is the fan turning on?
• Do you feel air blowing from the vents?

Let me know how things go.

Regards,

Gabriela

[plutokov]

Hi Gabriela, Happy new year!

Sorry for the delay. Is it safe to swap Y1 and G?

[GabrielaG]

Hi plutokov,

Thank you so much for keeping me updated. Happy New Year to you too! I appreciate you taking the time to perform the troubleshooting steps. I'm happy to continue assisting you right now. 

I understand you want to know if it is safe to swap the wires Y1 and G. We usually recommend this because it could help them avoid potential repair costs with a technician, but before proceeding with the wire swap, please turn off the power to their HVAC system at the breakers for your security and to prevent accidents.

Feel free to keep us posted if you have more questions.

Regards,

Gabriela