AC Suddenly Blowing Heat

[NestUserName22]

My Nest thermostat has been functioning correctly for a few years in controlling my heat pump. Yesterday, I turned on the AC and left the house. When I returned home, it was blowing only hot air and I got an email from Google that my system was on AC but the house got 8 degrees hotter.  I have not changed a thing from when it was functioning properly.  I assume it’s an issue with the Nest sending the wrong signal to the heat pump.  Does anyone know how to determine if the Nest is functioning properly or not, so I can focus my troubleshooting other parts of the system?

[Patrick_Caezza]

Was it in heat mode?

Do you have a heat pump or a conventional system?

[NestUserName22]

I have tried to run in both heat/cool and cool mode, but both of them were running in the “blue-screen” cooling mode. I have a heat pump with natural gas as the backup heat source. 

[Patrick_Caezza]

When was the last time that your system was serviced?

[NestUserName22]

Probably 10+ years ago. 

[Ryan_G · Accepted solution]

Hey folks,

Thanks for visiting the Google Nest Community. 

Since this thread hasn't had activity in a while, we're going to close it to keep content fresh.

If you have additional questions, feel free to submit another post and provide as many details as possible so that others can lend a hand. 

Hope this helps!

Kind regards,

Ryan

[MichaelHFarren]

After countless conversations with Nest, and NO HELP At all, i literally bought a new Honeywell Smart Thermostat. Everything works perfectly fine. Just like you, my wiring never changed, i just went to use Cooling a few weeks ago, and found only heat coming out. I have advanced HVAC knowledge know, and this is a Nest problem. Google wont acknowledge, or help with it. They just told me to buy a new one. Ha! Nope. Not doing that ever again.