Converting Nest Learning to Less Expensive Nest Thermostat

[dja1980]

I was trying to find the old thread I posted from 12/2020 where I received help installing a Nest Learning Thermostat.  Unfortunately, we had a small snake wrap around and short out a circuit board on our heat pump, and the HVAC tech told us our thermostat also needs to be replaced (will no longer switch the heat pump valve from Heat to AC).  Since we never used the learning features of the Nest Learning thermostat, I took advantage of our utility company's Black Friday $50 sale on the regular Nest thermostat.  Since the regular Nest thermostat uses less wires, I'm now wondering if I made a bad purchase.

Our system is a 2-Stage Electric Heat Pump with Auxiliary Natural Gas Heat (when outdoor temps drop below 40 degrees).  I wish I could find my old thread because someone helped me to identify the purpose of each wire.  Anyway, I'll post the photos below.  Is it possible to use the regular Nest Thermostat with my setup?

[dja1980]

I see other threads where photos are posted in the body of the messages, but I can seem to find how to do that.  I guess I'll just share the links for now...

https://photos.app.goo.gl/MkovxvGoDAZJekeQ9

https://photos.app.goo.gl/cdguRtC4mU1WRxK26

[Patrick_Caezza]

Your system is only compatible with the Nest Learning Thermostat, 3rd Gen.

If you try and use the Google Nest Thermostat, you will lose your 2nd-stage of cooling and some of your heating ability. Basically you are cutting your system heating and cooling ability by half.

[dja1980]

Thank for the reply... much appreciate!  This is what I needed.  I tried using the Nest Chat Support after I posted this.  I was told to cap the brown and black wires, but couldn't seem to get a straight answer as to whether or not I would lose some functionality by doing this.  I also watched some YouTube videos to try and make sense of what the different wires do.  I believe this is correct...

Red Marker (Rc) - Power
Blue (C) - Common (or Neutral)
Green (G) - Fan
Orange (O/B) - Electric Heat Pump Switching Valve
Yellow (Y1) - Electric Heat Pump Stage 1
Brown (Y2) - Electric Heat Pump Stage 2
White Marker (W2) - Natural Gas Furnace (outdoor temps below 40 degrees)
Black (*) - Emergency Heat (X2 on my old Honeywell thermostat)

When I switched the the 3rd Gen Nest from the original Honeywell thermostat back in 2020 (10 wires), I was told to cap and eliminate...

White (S1) - Outdoor Temperature Sensor
Red (S2) -  Outdoor Temperature Sensor

I'm still a little confused as to why there is an Auxiliary Heat (white marker wire) and Emergency Heat (black wire) when those 2 wires seem to result in the same action (turn on natural gas furnace).

Anyway, as you said, I think I'm going to have to purchase another 3rd Gen Nest Learning thermostat even though I don't like the aesthetics nor need the learning functionality the price tag commands.  I did leave the new thermostat installed last night, but found that it took a long time to warm the house at 8am this morning when the schedule bumped up by 3 degrees.  I assume I'll have similar issues cooling the house once we get to the peak of summer.  I guess the other option is to stick with this while we're in the mild spring season to make sure this does in fact fix the switching valve issue I started experiencing with the Nest Learning thermostat.  I'd hate to spend another $250, just to find out there an intermittent issue with the circuit board on the heat pump.

I'd love to think that Google will be coming out with an upgraded 8-terminal thermostat option at Google I/O in May since the 3rd Gen Nest Learning thermostat hasn't been updated since 2015 and still needs to be setup using the old Nest app, but I haven't heard on rumors on this... so not holding my breath!

[Markjosephp]

Hello folks,

I wanted to stop by and see how I could help.

Thanks for the help here, @Patrick_Caezza.

@dja1980, I appreciate your insight and for keeping up with the Nest Thermostats. Technically, your wiring configuration would work with the 3rd generation Nest Learning Thermostat, and temporarily disconnecting the auxiliary heat, emergency heat, and second-stage cooling for the Nest Thermostat 2020 model might help, but you'd lose your systems' functionality as a whole.

Please have a look at this article and let us know if you need more help.

Regards,

Mark

[Markjosephp]

Hi dja1980,

I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Jenelyn_O]

Hi there,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns, as I'll be locking this thread in 24 hours.

Best,

Jenelyn