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[Maki]

Hi 

I have an issue with my a/c not working on my nest thermostat. Also my heat wouldn’t come on unless I switch it to emergency heat. Does anyone know what the issue is? 

[CoolingWizard]

When you say “emergency heat”, This sounds like you have a heat pump type of system. On heat pump systems there is a 4-way reversing valve that changes the mode from Heat to Cooling or Cooling to Heat. The O/B terminal is the wire that energizes that valve to change modes. Did you by chance take a picture of the old thermostat and wires before you removed it? The Y terminal/wire  energizes the Compressor to start, Some Heat Pump systems default to Heat mode, and Some default to Cooling mode.  The wire you should have are:

R - 24VAC input from HVAC system

Y - For Cooling, energizes the contactor to start compressor

G - Indoor Blower Fan

O/B - Reversing Valve; changes system heat/cool mode. 
*Aux/E - Emergency Heat 

if you are not getting Heat or Cool, your not energizing the Y wire.  

Can you post a picture of the old thermostat and wires, and the nest wall pate and the wires?

[Ryan_G]

Hey Maki,

Thanks for reaching out here in the Google Nest Community.

I'd like to jump in here and check if you've seen CoolingWizard's response. We'll be glad to hear it from you and get a picture of the old thermostat and wires for us to further assist you.

Thanks for your help here, CoolingWizard.

Best regards,

Ryan

[Ryan_G]

Hey Maki,

I just wanted to follow up and see if you're still in need of help. Please let us know as we would be happy to answer any questions you may have. 

Best regards,

Ryan

[MelbaDT]

Hi, 

We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.

Best, 

Melba