Thermostat wiring

[Haroldc119]

I wanted to upgrade my thermostat to the Nest Thermostat but my current thermostat has 7 wires (red, orange, light blue, white, black, green and yellow). However , my nest thermostat has y, c, w, g, r and ob. (6 slots). How can I proceed with the installation

 

?

[CoolingWizard]

Your current thermostat has both Emergency Heat and Auxiliary Heat. So let us talk a little bit about those. Whenever a heat pump system is installed, they decided that they needed to have the ability for the homeowner to have some heat even when the compressor fails for some reason. They created the emergency heat connection. Now typically the emergency heat is wired to the exact same electric heat coils that the auxiliary heat is wired to. The difference is, the homeowner could activate emergency heat. They cannot activate auxiliary heat. Now the auxiliary heat exists so that the heat pump can create back up heat when it is in the defrost mode. Heat pumps in the winter will build up ice on the outdoor coil and they need to be able to melt that quickly. So what the heat pump does it temporary switches to an air conditioner, And pulls the heat out of the house to melt the ice quickly. When it does that it activates the auxiliary heat so that the air going into the house remains warm. 

if you want to be able to manually use an Emergency heat, you will have to upgrade to a Nest Learning Thermostat. For the Nest Learning Thermostat your wiring would be:

 Now then, if you want to go for the less expensive Nest Thermostat, you will not use the black wire that is your emergency heat.  

AC Cooling Wizard

[Haroldc119]

Ok. I think I got it. The emergency heat capability is not a necessity correcy? Furthermore, The home is actually in central Florida, I can't see why this feature would be necessary.  I just purchased the house! Thankyou very much.

[CoolingWizard]

@Haroldc119 , Yes in Florida you most likely would not need the Emergency heat capability.  You can go with basic Nest Thermostat and tape the black wire off.  

AC Cooling Wizard

[Markjosephp]

Hello there,

I wanted to ensure that everything was covered here.

Your help is much appreciated, @CoolingWizard. Very informative!

@Haroldc119 and @blkstar, I hope you've found the answer you're looking for. If you're still in need of assistance, feel free to let us know.

Regards,
Mark

[Markjosephp]

Hi folks,

I'm checking back in — how's it going? Still need our help?
 

Thanks,

Mark

[Markjosephp]

Hello everyone

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

Thanks,

Mark,

[blkstar]

as a add-on question, my current Braeburn 5220 thermostat, has 5 wires for a two stage AC/Heat system, RH, G, O/V R3, Y1, Y2, Trying to determine if the programmable google nest thermostat which uses 4 wires, which wire would not need to be connected, and thx in advance.

[CoolingWizard]

@blkstar ,

for your needs you must use a Nest Learning Thermostat 3rd Generation.  Your basic Nest Thermostat cannot support a heat pump with 2-stages.  

AC Cooling Wizard

[blkstar]

thx for that answer, which makes me wonder what is the difference, how can i tell a 1st or 2nd generation nest thermostat from the #3 generation thermostat?

[CoolingWizard]

Nest Learning Thermostat 2nd and 3rd Generation, have the high density 20-pin connector at the bottom of the base and 10 terminal connections. Y1, Y2, G, W1, W2/AUX, Rh, Rc, C, OB, and *.  The Nest Learning Thermostat E, also has the 20-pin connector but on has 6 terminals, Y1, W1, G, R, C, *OB connectors.  The basic Nest thermostat has Y, W, G, R, C, *OB and uses AA batteries there are 6 pins that connect into the base much like conventional thermostats. 

AC Cooling Wizard