Nest Thermostat won’t cool come spring year after year

[BCtn216]

Each spring when I need the AC, the Nest Thermostat won’t tell my HVAC to cool. I call the HVAC company for a tuneup and they say my HVAC system works great, but the thermostat’s “brain” is sending wrong messages. For the last few years I gone & bought a new thermostat, put it on the existing wiring, and the problem is solved. This year, I’m fed up and want a less expensive fix. I reset it to factory settings & it cools for a few seconds, then the heat kicks on. 

I have another Nest thermostat- from before Google bought them out. If I put this older thermostat on, it does work. It’s not my HVAC, it’s not the wiring, and a new thermostat (or my older Nest) does fix it for the summer. However, once we go through winter and the heating is used for months, the Nest can’t send the appropriate message to the HVAC system. What gives? I’m leaning towards giving up on Google-made Nest Thermostats and putting another brand on this unit. Anyone have a fix? I can’t believe this happens every spring! 

[CoolingWizard]

Surprise me when I see people think that the thermostat is communicating with their HVAC equipment. Thermostats do not ”talk” to the HVAC equipment.  The HVAC conventional thermostat is a simple device.  You set the desired temperature, you set the mode; heating or cooling, and the thermostat checks the ambient temperature, and if heating is needed, internally it connects the incoming AC power on R, and connects it to W. When the power arrives at the HVAC equipment, it starts the heating cycle.  If the mode is Cooling, if the temperature is above the set point, it connect the R to Y. This power arrives at the unit and starts the cooling cycle.   The thermostat is so simple. In fact that once the temperature is satisfied, it simply disconnects the R from the Y or the W.

When people are having problem with the nest thermostat, it typically is a problem with the schedule settings or the feature settings that they put in there without properly understanding how to set up the schedules or how to set up the ECO safety temperatures and things like that. If you really want to test the thermostats basic function, it’s very simple to do. Go into your device, say your nest app, and turn off all of the advanced features:

HOME/AWAY = Off

Auto Schedule = Off

Early On = Off

Cool to Dry = Off

Sunblock = Off

Airwave = Off

Set your ECO and Safety temperature to their Defaults.

Now, set you desired mode, in this case COOLING, then set your desired room temperature.   Monitor  your system and tell me how is behaving. 

The AC Cooling Wizard

[BCtn216]

I turned off all the advanced settings & it still heats when I set it to cool. I’ve had a Nest thermostat on this unit for 8 years. The original Nest thermostat still works great and performs heating and cooling as directed. I decided to get another Nest thermostat for my other unit 4 or 5 years ago at Christmas. It works fine the first year, but it has never been able to cool come the next spring so I just get a new one, then it works. If I take the Google Nest thermostat to the other HVAC, it won’t cool on this unit either. My HVAC tech tells me it’s the thermostat & won’t troubleshoot it since they install Honeywell devices, not Google. 

[CoolingWizard]

In order to best evaluate, the thermostat do use a volt, ohm meter and go to the compressor unit when the thermostat is in cooling mode set the temperature 3° or 4° below the current room temperature. Then go outside or to your air handler use a Volt ohm meter and see if there’s any current being supplied by the thermostat on the Y wire. Check between Y and C for AC Voltage.  If there is no voltage present, indeed, the thermostat is not sending the power. To verify this make sure that the conductor of the thermostat cable is not corroded on the Y wire. And make sure the wire is fully inserted to the point where the spring button on the outside remains pushed down.

The AC Cooling Wizard

[Jenelyn_O]

Hi folks,

Thanks for reaching out. I just want to check if you were able to proceed with the steps provided above? Please keep us posted.

I appreciate your help, @CoolingWizard.

Regards,
Jenelyn

[BCtn216]

I don’t see the need to run another test of HVAC system. I had our HVAC tech evaluate if the system works. It does & when I place an another Nest thermostat on the same wiring, the system will cool. Something is wrong with the little round circle (aka Nest thermostat). I’m just going to buy a new Nest or a different brand thermostat. Until then, I have another Nest thermostat I can grab from upstairs to cool the downstairs. 

[Jenelyn_O]

Hey BCtn216,
 

I understand. It can help us as well to isolate the issue further. If the issue would not occur with a different Nest Thermostat in the same location, therefore we can conclude that the original thermostat from that location is faulty. 

Please keep me posted.
 

Regards,

Jenelyn

[CoolingWizard]

Hello there, when you have your nest learning thermostat connected and when you go into SETTINGS > EQUIPMENT and the display shows the wires that are connected, does it show Y1 as connected?

AC Cooling Wizard

[Markjosephp]

Hi there,

We appreciate your continued support here. @CoolingWizard.

@BCtn216, how's it going? Have you managed to check your thermostat's wiring configuration? To better understand this, could you please share with us a photo of your thermostat's wiring?

Regards,

Mark

[Markjosephp]

Hi BCtn216,

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

Regards,

Mark

[Jenelyn_O]

Hi folks,

We haven't heard from you in a while so we'll be locking this thread if there is no update within 24 hours. If you need assistance or want to discuss topics, feel free to start a new thread.

I appreciate your help, @CoolingWizard and Mark.

Best,

Jenelyn

[BCtn216]

https://share.icloud.com/photos/0a6O_gQ-kv6E6uAANtziywf9g

[BCtn216]

Yes, Y1 is connected. I shared a link to a pic below

[CoolingWizard]

I see you have a heat pump system. Do you know if it is a B model or an O model?  O models are heating and you energize the OB wire along with Y1 to get cooling. Now then B models are cooling models and to get heat you must energize the OB wire along with Y1.  Which model do you have?

AC Cooling Wizard

[Markjosephp]

Hello there,

I wanted to ensure that everything was covered here.

Thanks for your expertise @CoolingWizard, and your assistance, Jenelyn.

@BCtn216, how's it going? Have you managed to configure your heat pump's orientation? I did find a helpful article with some troubleshooting steps; let us know how it goes.

Regards,
Mark

[BCtn216]

Mark, I’ve read those instructions and it doesn’t fix the cooling issue. I’ve had my system evaluated by my HVAC tech and they system is functioning normally. If I put a new Nest thermostat on it, it works just fine. I’m just tired of having to buy a new Nest every year.  Seems like a software glitch to me. 

[BCtn216]

It’s an O model

[CoolingWizard]

Ok, then by default it is a heating model and requires the OB wire energized to switch to cooling.  In my HVAC business I have installed hundreds of Nest thermostats and never have I seen a problem like you are having. It makes no sense that you install a new thermostat and 12 months later the cooling does not work.  If indeed your Nest thermostat is configured properly to match your HVAC equipment, then we need to escalate this case and get your defective Nest thermostats including your baseplates returned to engineering.  The engineering team needs to evaluate the failure on the OB connectors.   Think about it, multiple thermostats fail with the OB wire terminal only. 

AC Cooling Wizard

[Markjosephp]

Hi there

I wanted to ensure that everything was covered here.

Thanks for the additional input, @CoolingWizard.

@BCtn216, I appreciate all the steps you've taken. We'd like to take a look at this for you. Could you please fill out this form with the needed information? A member of our higher-tier team will be in touch over email to help.

Let me know once you're done.

Best,
Mark

[Dan_A]

Hey there BCtn216,

We haven't received your form. Have you had a chance to fill it out? Just in case here's the link.

Kind regards,

Dan

[EmersonB]

Hi everyone,

@BCtn216, we got your form — thanks for filling it out. Our team will reach out to you via email to further assist you. If you have any questions or concerns, feel free to create a new thread as I will be locking this thread after 24 hours.

I appreciate the help, CoolingWizard, Jenelyn, Mark and Dan.
 
Regards,
Emerson