AC blowing Heat

[BoCung]

Installed 2 Nest Learning thermostats in my vacation home last winter. The downstairs thermostat works fine but the upstairs one has problem. On that thermostat, heat works fine on heat mode, but when I switch to AC, it  blows hot and cold air. I had to unplug the white wire from the W1 post on the thermostat to stop hot air from blowing. Will plug it back in when I need to heat the upstairs room I guess.

[zoeuvre]

Hi BoCung, 

Yikes! I'm sorry to hear that your Nest Learning Thermostat blows heat when is set to cool. Let's see what's going on. 

1. Are you located in North America or Europe?
2. Did you try using the Help Center or troubleshooter before contacting support? If so, which steps have you tried already?
3. When did cooling last work?
   • If newly installed
     • Check compatibility using the Compatibility Checker tool.
     • Gather all details of the old thermostat & HVAC system.
     • Check the make and model of the cooling and heating system, including the make and model for the, fan-coil or air-handler units.
     • Check if the HVAC system might be using a multi-speed or variable speed fan.
   • If not newly installed, was it working before?
     • Check for any recent changes to the HVAC system or servicing made.
     • When was the last maintenance service and cleaning?
     • Is this the first time you’re calling for cooling this year?
       • If yes, did heating work without issues in the winter?
4. What type of system do you have? (Heat Pump or conventional type)
   • For Heat Pump:
     • Did you check O/B wire configuration and tried changing the O-wire to B-wire configuration or vice versa?
   • For conventional type:
     • Did you verify if Fan and Heating still work?
5. Did you  turn off the power to your HVAC system?
   • Are the breakers turned on?
   • Did you recently experience a brownout or blackout?
   • Did you have any construction or maintenance work done on your home?
6. Do you have a photo of your old thermostat? Make sure your Nest Thermostat is wired correctly and verify that the display is receiving power.
7. Did your utility company install a box on your HVAC system that turns the system off during high demand (peak) times to save energy? 
   • Are you the homeowner or tenant?
8. Do you see a power code on your thermostat?
9. Have you set up a temperature schedule for your thermostat?

I'll look forward to your response. 

Best,

Zoe 

[BoCung]

1. Are you located in North America or Europe? Yes
2. Did you try using the Help Center or troubleshooter before contacting support? If so, which steps have you tried already? None of the Q&A on Help Center works
3. When did cooling last work? It worked before I installed the Nest thermostat. After installtion, it blows hot and cold air when it's on cool, and blows heat only when set on heat.
   • If newly installed New house, new AC. I just changed the builder-installed thermostat to Nest and that when it started blowing hot and cold air when set on cool. 
     • Check compatibility using the Compatibility Checker tool.
     • Gather all details of the old thermostat & HVAC system.
     • Check the make and model of the cooling and heating system, including the make and model for the, fan-coil or air-handler units.
     • Check if the HVAC system might be using a multi-speed or variable speed fan.
   • If not newly installed, was it working before?
     • Check for any recent changes to the HVAC system or servicing made.
     • When was the last maintenance service and cleaning?
     • Is this the first time you’re calling for cooling this year?
       • If yes, did heating work without issues in the winter?
4. What type of system do you have? (Heat Pump or conventional type)
   • For Heat Pump:
     • Did you check O/B wire configuration and tried changing the O-wire to B-wire configuration or vice versa?
   • For conventional type:
     • Did you verify if Fan and Heating still work? Yes
5. Did you  turn off the power to your HVAC system? No
   • Are the breakers turned on?
   • Did you recently experience a brownout or blackout?
   • Did you have any construction or maintenance work done on your home?
6. Do you have a photo of your old thermostat? Make sure your Nest Thermostat is wired correctly and verify that the display is receiving power. I installed two Nest. Downstairs one works great, upstairs has problem. Nothing wrong with the wiring. I believe I have a defective Nest.
7. Did your utility company install a box on your HVAC system that turns the system off during high demand (peak) times to save energy? No
   • Are you the homeowner or tenant? Homeowner
8. Do you see a power code on your thermostat? No
9. Have you set up a temperature schedule for your thermostat? Not yet

I'll look forward to your response. 

[Markjosephp]

Hey folks,

I'm chiming in to make sure everything is covered here.

Thanks for the help here. Zoe.

@BoCung, we appreciate the details. It may be too much to ask, but this would help us isolate the issue. In addition to what was asked above, can you share with us a photo of your old upstairs thermostat and your current thermostat's wiring setup? What type of furnace do you have? (gas, electric, etc.). Also, do you have two separate HVAC systems for your two Nest Thermostats? If they both have the same version, have you tried swapping them, and were there any differences?

Keep us posted.

Regards,
Mark