Fan won't turn off

[Dwein1107]

Hi Everyone - 

I've seen many posts about this, but the resolution of adding a C wire does not seem to be the fix for me. I have had the 2nd Gen Learning thermostat running since January but as of yesterday, the fan will not turn off. I have turned off all the eco modes, smart/home/away things to try to isolate but the fan just will not stop running even when A/C is not cooling. Here are some steps I have already taken to troubleshoot

1. Turn off thermostat
2. Take thermostat off the wall

If I kill the power to the furnace/blower, it stops the fan. The moment I flip power back on, the fan starts. 

Something interesting that may help diagnose... If I actually turn the fan on with the thermostat/app, it lowers the fan speed/output. Once I turn the fan off, the speed/output kicks into a higher gear - even though the fan should not be running at all. 

Image of my thermostat wiring is attached if it helps. Appreciate any guidance! 

[Dwein1107]

As a follow up of trying to self troubleshoot - I disconnected the G (green) wire which is the fan wire I believe, but when turning the power back on, the fan is blowing again. I think there's a story to be told between the fan speed/gear I mentioned in my first post. When the fan is actually "on" that I turn on, it slows the fan down. When off, the fan speeds up. 

I have seen some other posts that without a C-wire, the fan runs to power the thermostat but when I wired this, I combined wires to make a C-wire so don't think that should be the issue. 

[Markjosephp]

Hello Dwein1107,

Thank you for taking the time to let us know about your inquiry. Let's sort this out.

This is most likely a power-related issue that needs to be checked. A question: does the same issue occur even when a C-wire is installed? Please gather your thermostat's power readouts in the Technical Info settings with and without the Common wire.

Note: Turn off the power from your HVAC system at the breaker box first before touching the wire.

Keep me posted.

Regards,
Mark

[Markjosephp]

Hey there,

Checking back in — how's it going? Still need our help?

Thanks,

Mark

[Markjosephp]

Hi Dwein1107,

I'm checking in to make sure that you've seen my response. Please let us know if you have any additional questions or concerns before we close this thread in 24 hours. 

Best,

Mark