Compatability

[Jstncnnll]

By going through the install procedures on the home app, it says my current thermostat is not compatible. I have C,B,R,G,Y and E with a jumper from E to AUX. But after talking with Google support and giving them my units make ad module number, they said it IS compatible, but that I had to talk to an HVAC tech or nest pro "as I have a change over valve (B wire) with conventional system". I talked to a tech and they have no clue what that means. But he suggested I hook up by matching all the wires except put the E wire into W on the new base. After trying that, my AC and Heat work, but my emergency heat blows cold. Which makes me think my AUX heat would also blow cold? So the question is, what would I need to change to make my wiring compatible since that seems to be the only issue.

[Houptee]

B wire means you have a heat pump which has a outside "reversing valve" that changes the flow of the freon gas when you select heat.

Do you have Aux heat or Emergency heat? They are different things.

Did you tell the nest you had a heat pump with Aux Heat or Emergency heat during setup?

Read this info

https://support.google.com/googlenest/answer/9276120#zippy=%2Chow-to-tell-if-your-system-has-emergen...

[Jstncnnll]

My original thermostat had a wire going to E for the emergency heat with a jumper from E to Aux. 

When I go to the wire configuration under settings, thermostat, wiring, it says 

• Y - Heat/Cool
• C - 24v common
• W - Aux, Heat
• G - Fan
• R - Power
• *OB - Heat Pump

[Houptee]

On the old Tstat when you felt cold did you flip a switch to turn on your emergency heat manually or did the system kick on the Aux heat automatically? 

Im trying to explain that Aux heat and Emergency heat are different things so first you need to tell us what you have.

[Jstncnnll]

Emergency heat was manually switched. AUX was automatic. 

[Houptee]

Is this a heat pump with a gas furnace as backup heat, or is it electric heating coils that kick on in emergency heat mode?

[Jstncnnll]

It is an electronic system with heat coils.

[Houptee]

Can you go to the equipment and look at the thermostat wires and take a clear picture of the colors and screws with the labels of the screws on the equipment.

Also there is usually a wiring diagram decal on the inside cover on the system showing thermostat wiring.

Take pic of that wiring diagram and post it.

Or if that is not possible post the Brand and model number of the indoor unit and look up on Google the wiring diagram for it.

[Jstncnnll]

 here is the picture of the original thermostat wiring. Is that what you needed?

[Houptee]

We need to see the wires on the equipment to see what those wires are connected to.

Go to the indoor unit and take cover off and you will see those same color wires attached to screws.

[Jstncnnll]

Sorry, I was at work. Here's the wiring diagram on the furnace. 

 

[Houptee]

White wire should go to W1 according to the wiring diagram.

The diagram does not show a B wire are you sure this is a heat pump?

A heat pump runs the outdoor AC unit in both cooling mode and heating mode.

Looks like you have a AC system and electric heat but not a heat pump.

Only way to be sure is look at the wires on the furnace and do you see the Blue wire connected to anything at the furnace?

[Jstncnnll]

 here's the wiring inside the furnace. The blue wire comes out from the thermostat wire, then connects with an identical wire leading to outside the house.

[Houptee]

Not sure if you have a heat pump so only thing I can suggest is get the make and model of the indoor unit, and go outside get make model of outdoor unit.

Look up on the internet the outdoor unit model to see if it is a heat pump or just a regular AC unit.

If it is just a AC system with electric heat for winter (not a heat pump) then you can try disconnecting the B blue wire on the Nest and change the system type to let the Nest know you have ac with Electric heat.

[Jstncnnll]

When I turn my heat on on the thermostat, the outside unit turns on as well.

[Jstncnnll]

Also by googling the make and model, it is in fact a heat pump.

[Houptee]

OK then the blue B wire must go directly outside to the unit after the wire nut splice inside.

Do you have more than one thermostat for the system? 2 zones? There seems to be a lot of wires connected with wire nuts.

[Jstncnnll]

Only 1 thermostat. 

[EdwardT]

Hi folks,

@Houptee, thanks for the help!

@Jstncnnll, how's it going with your Nest Thermostat? Were you able to set it up? Keep us posted.

Thanks,

Edward

[Jstncnnll]

It's set up and the air and heat work, I just can't get the emergency heat to work and not sure if the Aux heat works or not.

[Houptee]

Did you put white wire in W (heat wire) on Nest?

Does the Nest show it see the W wire?

Did you tell the nest that W was auxiliary heat?

Aux heat is not the same as Emergency heat.

Aux heat turns on along with the heat pump still running.

Emergency heat is for when the heat pump is broken down you can switch to emergency heat and it shuts off the heat pump (outdoor unit will not run in Emergency heat mode). It only runs the heat coils and the fan.

Your old tstat had Aux and Emergency heat jumpered together on the white wire so you only have one set of heat coils that get turned on when 24v is applied to the white wire.

[Jstncnnll]

Yes, the nest reads the wires as follows;

• Y - Heat/Cool
• C - 24v common
• W - Aux, Heat
• G - Fan
• R - Power
• *OB - Heat Pump

White wire is in W and reads as Aux heat. Blue wire is in *OB for heat pump. Honestly, I live in the south so as long as the why it's wired won't damage anything in the long run, I can live without the emergency heat.

[Houptee]

It is probably working but if the heat pump can heat the house it doesn't turn on the coils.

You can change the settings for when it kicks on the coils its called Heat Pump Balance.

Read this article how to fine tune the way it uses Aux heat.

https://support.google.com/googlenest/answer/9248719#zippy=%2Chow-to-change-heat-pump-balance-settin...

[Markjosephp]

Hi there,

Thanks for helping here, @Houptee.

@Jstncnnll, I wanted to ensure that everything was covered here. If there’s anything else we can help you with, please let us know.

Regards,

Mark

[Jstncnnll]

No, I just left it as is and so far no issues. Thanks for the assistance. 

[Markjosephp]

Hi Jstncnnll,

Sounds great! Thanks for the update. I'm glad that it's working smoothly. We can probably consider this one finished, so I'll close the thread in 24 hours unless I can help with anything else. 

Thanks,

Mark