Nest Learning Thermostat wiring

[BrandonLi]

I am currently replacing the old Honeywell thermostat with the nest learning thermostat. But compared with the regular 5-wire thermostat, I have more wires as follows: 

The current wiring

There are 8 wires in total:

1. y2/w2 are jumped

2. white wire is connected to the terminal w2

3. green wire is connected to the terminal g

4. orange wire is connected to the terminal w

5. the blue wire is connected to the terminal c

6. the yellow wire is connected to the terminal y

7. the red wire is connected to the terminal r

8. the black and brown wires are not connected to any terminal

In this case, how to connect the wires to the new nest learning thermostat?

[CoolingWizard · Accepted solution]

hello Brandon,

What you have is a heat pump system. The wire labels are the ones on the bottom of your thermostat base and the white jumper between what you think is Y1  and Y2 is actually a jumper between auxiliary heat and emergency heat. The heat pump in the winter time when it’s in heating mode can gather ice on the outdoor coil and it has to go into what they call defrost mode. When in defrost mode, it changes the reversing valve (OB) to use the heat from inside the house to warm the outdoor coil and melt the ice. Basically it Ia put into air conditioner mode. When it’s doing this, the defrost control board on the outdoor unit will turn on the auxiliary heat on the inside air handler to keep the air from getting cold going into the house. Your old thermostat had ability to manually turn on the emergency heat. Now it’s wired to the exhilarate heat. Emergency heat is used when the outdoor unit fails and they have to wait for repair. The thermostat can manually put the system into emergency heat so there’s some heat in the house. 
Your Wires are:

White Wire is AUX, this is auxiliary Heat

Green Wire to G, this is the Indoor Blower Fan

Orange Wire to O/B, this is the Heat Pump Reversing Valve. 
Blue Wire to Common (C)

Yellow Wire to Y or Y1 this is outdoor Compressor control

Red Wire, this is Power Input connect to R or Rc.

You will need a Nest Learning Thermostat 2nd or 3rd generation.  With this model you will be able to set up both Auxiliary Heat and Emergency Heat.  To do this you will have to do a little wiring in the indoor unit to use the black wire that’s not currently being used and connect that to emergency heat. Do you have access to the indoor air handler?

The AC Cooling Wizard

[CoolingWizard · Accepted solution]

hello Brandon,

What you have is a heat pump system. The wire labels are the ones on the bottom of your thermostat base and the white jumper between what you think is Y1  and Y2 is actually a jumper between auxiliary heat and emergency heat. The heat pump in the winter time when it’s in heating mode can gather ice on the outdoor coil and it has to go into what they call defrost mode. When in defrost mode, it changes the reversing valve (OB) to use the heat from inside the house to warm the outdoor coil and melt the ice. Basically it Ia put into air conditioner mode. When it’s doing this, the defrost control board on the outdoor unit will turn on the auxiliary heat on the inside air handler to keep the air from getting cold going into the house. Your old thermostat had ability to manually turn on the emergency heat. Now it’s wired to the exhilarate heat. Emergency heat is used when the outdoor unit fails and they have to wait for repair. The thermostat can manually put the system into emergency heat so there’s some heat in the house. 
Your Wires are:

White Wire is AUX, this is auxiliary Heat

Green Wire to G, this is the Indoor Blower Fan

Orange Wire to O/B, this is the Heat Pump Reversing Valve. 
Blue Wire to Common (C)

Yellow Wire to Y or Y1 this is outdoor Compressor control

Red Wire, this is Power Input connect to R or Rc.

You will need a Nest Learning Thermostat 2nd or 3rd generation.  With this model you will be able to set up both Auxiliary Heat and Emergency Heat.  To do this you will have to do a little wiring in the indoor unit to use the black wire that’s not currently being used and connect that to emergency heat. Do you have access to the indoor air handler?

The AC Cooling Wizard

[BrandonLi]

Hi, there,

My model is Nest Learning Thermostat. (P.S. I live in Florida, I cannot believe it has such a "luxurious" heating system).

Cheers,

Bowen.

[BrandonLi]

The heating system is not in a such hurry in my current area (Florida),  in this case, can I still pass the black wire?

[CoolingWizard]

If you feel comfortable working with your air handler, then I would suggest you use the black wire as your E wire. You will need to turn the power off to your air handler, look at it closely and see what part of the air handler does the brown thermostat cable go in. That’s the panel you wanna open. Once you open it, you’ll see those wires that are connected to either a control board or wire nuts. Do you want to take the black wire follow it to the control board and see where the E terminal is. Attach the black wire to the E terminal on the control board. Put the doors back on turn the power back on. Your thermostat attach the black wire to E. Now you will have the ability to mainly turn on emergency heat. If your outdoor unit should ever fail and you require service there in the winter time.

I hope this helps you.

From the desert area of California,

The SC Cooling Wizard

[CoolingWizard]

Here I believe the  Answer from @Patrick_Caezza is incorrect about the Nest software operation of Auxillary Heat. The auxiliary heat is controlled by the defrost board located in the heat pump outdoor unit.  The only additionally heat the user can manually activate is the Emergency Heat option.  This is why the nest learning thermostat includes the E wire location.  Most heat pump air handlers do not have an E terminal. Depending on the brand the E wire at the thermostat is cross-connected to the W2 along with the W2 on the Heat Pump Defrost Control Board. This is the Auxiliary Heat and having the E wire cross-connected enables a homeowner to activate the Emergency Heat thus turning on the Auxiliary heating.

This is the reason I suggested to use the black wire as the E wire and make the cross-connection with the AUX wire in the Air Handler. Brandon if would like to understand how that connection will need to be accomplished just ask me @CoolingWizard 

The AC Cooling Wizard

[Patrick_Caezza]

@CoolingWizard 

No, I am not wrong.

I have provided the correct option for wiring the Nest Learning Thermostat into the OPs system.

[Markjosephp]

Hello folks,

I'm chiming in to ensure that everything was covered here.

Thanks for all the inputs, @CoolingWizard and @Patrick_Caezza

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

Regards,

Mark

[Jake]

Hey there,

I wanted to check in and see if you are still in need of any help. Please let me know, as I would be happy to assist, and answer any questions you may have.

Best regards,
Jake

[Jake]

Hey there,

I want to ensure you are good to go, and everything is working properly. Please let me know if you are still having trouble, as I will be locking the thread in 24 hours due to inactivity.

Best regards,
Jake

[Patrick_Caezza · Accepted solution]

@BrandonLi 

The jumper between the E and Aux terminal on the original thermostat is only there, so you can manually turn on the Aux heat if you need it.  You'll likely find no E terminal in the Furnace/air handler. You can just remove it. as it is not needed.

Since you have a heat pump I would suggest wiring it like this.

White - AUX to W2 (set as AUX heat) Jumper to E not needed)

Green - G to G

Orange - O/B to OB

Blue - C to C

Yellow - Y to Y1

Red - R to Rc (jumper to Rc not needed)