Need help with Nest Thermostat 3rd generation wiring

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Old 11-27-18, 05:12 PM
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Need help with Nest Thermostat 3rd generation wiring

Hello,
I am attempting to install a nest third generation thermostat. I have been able to install it but when I set the heat only cold air is blowing through the vents. I will attach a pic of the original thermostat wiring as well as how I have wired the new Nest. Any help would be greatly appreciated. Thank you, Carolyn

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Last edited by PJmax; 11-27-18 at 05:17 PM. Reason: cropped/reoriented pics
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Old 11-27-18, 05:18 PM
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Welcome to the forums.

Your wiring is correct.
You must tell the nest that you have a heat pump system with no back up or AUX heat.
You are also using O in O/B. (Unless you have a Rheem or Ruud outdoor condenser in which case you will using B in the O/B setting).
 
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Old 11-27-18, 06:08 PM
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I see an unused orange wire in the background. Maybe the white wire really is a W and should be moved to W1 on the Nest?
 
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Old 11-27-18, 06:20 PM
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Could be. There's a blue wire floating around back there too.
 
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Old 11-27-18, 06:33 PM
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Thank you for your reply. I have a gas furnace but on the nest it reads Y1 Type: heat pump heat/cool, Source: Electric and I dont know how to switch it to gas or if that makes a difference and delivery says forced air. I have tried both O and B and still get cold air being blown out.
Should I switch the yello wire to Y2?
Again thank you for your help.
Carolyn
 
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Old 11-27-18, 06:36 PM
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That could be, the white wire in the original wiring was in the spot where it read W on top and O/B on the bottom. What is the difference? Thank you, Carolyn
 
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Old 11-27-18, 07:29 PM
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The top letters are for conventional systems like gas furnace. The bottom letters are for heat pumps. The Honeywell thermostat had one one terminal that handled both types of systems - you program the thermostat to tell it what the terminal is. An O/B terminal tells the heat pump to heat or cool. A W terminal directly turns the furnace on and off.

Move the white wire to W1.
 
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Old 11-27-18, 07:39 PM
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The nest configuration should change. It may now read gas furnace and A/C.
You may have to tell it Gas - forced air.
 
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