Nest 3rd Gen Aux Heat Not Working - cold air

[WillR]

Help us @CoolingWizard Kenobe. You are our only hope.

- nest 3 rd generation

- heat pump with forced air (works fine both heating and cooling)

- secondary source / aux for lower temps is electric furnace in attic.

system is set to switch to aux heat at 28 degrees. When it switches over (or when system is tested) only cool air is blown from the electric furnace.

wiring is correct according to Nest install with electric furnace connected through W2 wire. I would think heating element of furnace is broken and except when old thermostat is connected six heat works just fine.

set up as dual fuel with electric forced air as aux heat.

any suggestions?

Thanks.

[Markjosephp]

Hello WillR,

I'm sorry for the trouble this may have caused you — let's see what's going on and why your system only blows cool air when aux heat is activated.
 

I'd love to know more about this. Could you share a photo of your current thermostat's wiring? Also, have you tried the steps in this guide? Please let me know if that helps, or if the issue still persists.
 

Thanks,

Mark

[Jhonleanmel]

Hey folks, 

We appreciate your help here, @Markjosephp.
@WillR, I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

[WillR]

Hi Mark. Thanks for the reply. The heat pump is not the issue. When the system switches to aux heat for lower temperatures (with this breakpoint set in Nest settings) the aux heat does not blow warm air. It does with old Honeywell thermostat. 

thanks. 

[WillR]

Adding picture to previous reply. Thanks. 

 

[WillR]

@CoolingWizard  any thoughts here?

[CoolingWizard · Accepted solution]

WillR,

I have found that sometimes the nest configurator tool will put the auxiliary heat on W1 instead of the AUX when defining a heat pump. We need to check the nest thermostat itself to see what it current has defined. There are a few steps to do this, and here are the steps.
1. Go to the nest thermostat and tap the screen to rotate the dial to SETTINGS and tap to select.

2. Now rotate the dial until it gets to EQUIPMENT and select. You will now see a back plate display showing the wires that the thermostat has detected. Just make sure all your wires are detected.  Select Continue. The next screen will the you your system the thermostat is controlling. It should show Heating-Cooling-Fan. Choose Continue and select..

3. At this point, you will see equipment, settings, Done, Heat Type, Pro Setup, and Back. We are going to choose Pro Setup. We will then get a warning screen, saying how bad it will be If you don’t do this right, just choose Continue and select.

4. At this point you will again see what looks like the backplate for each of those wires and you’ll see either a green wedge or a yellow wedge. If you have all greens we’re doing good if any of them are yellow, we need to fix. To fix a yellow wedge rotate the dial to the yellow wedge and select. You will now see that defined position such as Aux or W1 and you can now rotate the dial to this SOURCE and select. Once selected, you can rotate the dial and choose the source  and for you choose Electric. Press the display and select that. The next one down is called delivery and yours should say Forced Air. And the last one is fan and it should say Don't Activate. A little about this fan. On older HVAC systems  the thermostat controls the blower fan. At the same time you chose the heating function the thermostat also activated G too. Now the newer systems, such as your heat pump, have an integrated furnace control board that will take care of the fan so that’s why we select Don’t Activate. Choose Done, and select. 
5. you should now see the back plate with the green and wedges, and now it should all be green and all be defined. Select Done a few times and you should be ok.

Ken, The AC Cooling Wizard

[WillR]

Ken. Thank you for the detailed response. I feel confident the Nest is now set up correctly. 

[EdwardT]

Hi folks,

@CoolingWizard, thanks for the help!

@WillR, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[WillR]

All set. Thank you. 

[EdwardT]

Hi WillR,

Thanks for the update. I'm glad to hear that everything is set up. I will be locking this thread in 24 hours. Please feel free to create a new thread should you have some more questions or concerns in the near future and we'll be more than glad to help.

Thanks,

Edward