topic Re: Nest Gen 3 turns off and back on within a few seconds in Nest Thermostats

Nest Gen 3 turns off and back on within a few seconds

Engineer — Sat, 16 Jul 2022 04:48:20 GMT

There are multiple recent threads regarding the Nest thermostat turning the air conditioning system off when it shouldn't and then back on within a few seconds. Have the people at Nest acknowledged this issue? I am running a C wire.

Re: Nest Gen 3 turns off and back on within a few seconds

TROBBS — Sat, 16 Jul 2022 08:51:34 GMT

My system did the same thing. Existing t-stat controlled A/C , installed Nest and the forced air heat worked but A/C kicked on and off within seconds.

I did have a blue "C" wire on old t-stat, and used that on Nest. Unfortunately the common wire was wired incorrectly on the control board. I switched it to the correct terminal and A/C works perfectly.

Re: Nest Gen 3 turns off and back on within a few seconds

wyounger — Sat, 16 Jul 2022 19:58:22 GMT

+2 on this issue. I have two learning-type Nest 3’s (two single transformer gas/electric split systems) and both started doing occasional 5-second off cycles of the AC compressors this year after working fine last year. Each one does it once or twice a day, often within a few minutes of 10am or 10pm. They don’t do this in sync, and they act like the AC should not be cycling off (10 am and 10 pm are just before/after my peak electric rates, so the ACs are supposed to run for a few hours nonstop then based on set points; and no, I don’t have a temperature change programmed for 10am or 10pm, and I don’t use the learning function because that turns out to be problematic when the whole world is switching to time of use electricity rates). Both systems were power stealing, but once I started noticing this issue, I had the C wire on one of them connected when this started happening, and it might have resolved it. I don’t think it’s an inherent problem with power stealing, I think somebody broke the firmware in the last update at a place that might have only affected power stealing. My thermostats have no issue getting enough power, batteries are at 3.7 volts, etc. , and these systems are running in cooling mode for 6-12 hours a day.

Google, this is a VERY serious issue. Short cycling like this is destructive to AC compressors, contractors, and wiring. Most are physically incapable of restarting with less than 2-3 minutes of off time prior. Attempting that restart causes a huge power draw when the compressor motor tries to start but the refrigerant pressures block it from turning (“locked rotor). There is fail safe logic in every digital thermostat since the 1980s that prevents short run cycles and short stop cycles on compressors because that behavior kills major components. If this isn’t fixed soon, Nest’s image in the HVAC industry will not be repairable.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Wed, 20 Jul 2022 03:08:29 GMT

Anybody from Nest have any answers? At this point, I would be happy with an answer of "we don't know".

Re: Nest Gen 3 turns off and back on within a few seconds

wyounger — Wed, 20 Jul 2022 16:41:06 GMT

I connected my C wires (both ends) and it seeeeeems like it might have fixed it. Hard to tell but I have not heard the issue since; will be more sure after being home all weekend and having more time to hear any recurrence.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Tue, 26 Jul 2022 04:43:32 GMT

I guess Nest is telling us, indirectly, to go buy a thermostat from their competitor. They're not leaving us much of a choice.

Re: Nest Gen 3 turns off and back on within a few seconds

wyounger — Tue, 26 Jul 2022 20:04:38 GMT

I have not noticed either of my systems having this malfunction in the couple weeks since I connected the C wires. Their lack of responsiveness to a widespread issue has definitely ended my recommending Nest to others, though.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Wed, 27 Jul 2022 00:29:15 GMT

I have a Nest 3 in my home and one in an apartment I rent for work. I don't know about the apartment, but my house is running the C wire. Both applications short cycle the compressor, and the thermostat does not always run the delay timer. I've rebooted both of the thermostats multiple times with no benefit. I've already started searching for a replacement thermostat.

Re: Nest Gen 3 turns off and back on within a few seconds

Ryan_G — Thu, 28 Jul 2022 06:03:01 GMT

Hi everyone,

Thanks for sharing your experiences here in the Google Nest Community and we're sorry for the delay.

With this behavior from the AC or furnace, there are things that we could check for us to further isolate the issue. First, the common wire, though it is not available to all systems, but it is an important wire for the Nest Thermostat. The C wire is responsible for giving your Nest Thermostat constant and enough power to function properly. That's what wyounger have done and it seems to make it up and running, thanks for sharing your thoughts here too, wyounger.

For the others, I'd like to further assist you by checking if there's an unused wire that can be used as a C wire.

Best regards,

Ryan

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Thu, 28 Jul 2022 06:20:50 GMT

Hi Ryan,

Since the initial installation of the thermostat, I did not use the C wire. I have since added it approximately 4 weeks ago and have noticed no difference in performance.

Re: Nest Gen 3 turns off and back on within a few seconds

Ryan_G — Thu, 28 Jul 2022 11:12:03 GMT

Hey Engineer,

The C (common) wire serves as a constant power supply to your Nest Thermostat. For it to be connected all the time and to efficiently controls your HVAC system.

Regards,

Ryan

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Thu, 28 Jul 2022 13:35:19 GMT

Thank you for the reply, Ryan. I'm not exactly sure what to do with the information you just gave me. It almost sounds like you're saying the thermostat will not work without the common wire. I'm sure you are aware the thermostat will work without it by grounding through a resistor and returning on one of the other wires.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Thu, 28 Jul 2022 13:56:25 GMT

Hi Ryan,

The following pictures may help show at least some of the issues that I am finding. In the first picture, you'll notice the history from the app is saying that the thermostat has adjusted itself in order to get to the set point by a certain time. I do not use this feature; it is turned off. The time that is shown is the time when my schedule was making a change:

The next picture shows a scheduled temperature shift going down at 11:45 p.m. on Monday 25. The set point change was from 74° f to 68° f. Shortly into Tuesday 26, the system shut off for no apparent reason; the target temperature was not yet achieved, so there's no obvious reason for the system to have stopped. When this occurs, the thermostat will sometimes invoke the delay feature in order to protect the compressor, but this is not always the case. Sometimes, it will turn off for a second or two, and then turn back on. This has disastrous consequences for the compressor motor and it's controlling electronics.

Hopefully the above information will assist Nest in understanding why the system frequently short cycles.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Thu, 04 Aug 2022 03:02:33 GMT

I think I found a solution! I should be receiving this next week!

Re: Nest Gen 3 turns off and back on within a few seconds

usalbeash — Sat, 06 Aug 2022 14:35:36 GMT

I bought a 25$ thermostat and installed it and it has worked fine since. I spent last on a chat night on a chat with 2 people from nest. They had me switch my Y1 wire with my W1 wire and then turn the heat on. Which really turns the Air on. I did this for an hour and it never shut off. So there solution, once again, was for me to run A “C” wire saying it isn’t getting enough voltage to keep the battery charged in the NEST. Good luck this was my last 250$ lesson with NEST. I will tell everyone not to waste the money

Re: Nest Gen 3 turns off and back on within a few seconds

horseshoehorn — Sun, 07 Aug 2022 17:12:11 GMT

This is an infuriating response. Nest very clearly advertises the Gen 3 as a thermostat that does not require a C wire. Nest is either misleading in it's advertising or there is a problem with the thermostat that is not being acknowledged.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Sun, 07 Aug 2022 17:45:18 GMT

I used my thermostat for about 3 years with no C wire and had no issues. It was not until this past May when there was a software update that I noticed things going sideways. I don't believe this has anything to do with using the C wire or not.

Re: Nest Gen 3 turns off and back on within a few seconds

wyounger — Sun, 07 Aug 2022 18:02:29 GMT

I partly agree. Something changed. I have two Nests that worked perfectly for a year (installed last July), then both suddenly started having this problem in June or July this year. They were running in power stealing mode (no C wire), and connecting an unused conductor in each furnace to start acting as a C wire seems to have fixed it. But I think they were getting plenty of power all along; the internal battery voltage in each Nest is hardly any different now running with C as it was historically without C (3.7 volts or more then, 3.8 volts now). It's got to be that the problem was introduced in firmware update.

For any that have spare wires in the bundle running from the thermostat to your furnace/air handler, all you need is for one of those wires to be connected to the C terminals on both ends (use blue if you have one). I believe all furnaces and air handlers have the C terminal, but back in the day (or in more recent times if your installer was old-school) there was no reason to connect it, so often they just didn't. Older thermostats did not use power, and so C wires didn't become important until we got far enough into digital/programmable thermostats that we realized that running thermostats on AA batteries was a dumb solution, Since Nest seems to be caught with their pants down on the firmware problem and the user community would like to solve this before Nest pull them up or your AC compressor grenades, connect up those C wires on both ends. If you don't have a spare wire (older installs may only have 4 or even 2 instead of the more-modern 7), you can either pull new 7-conductor wire or HVAC techs may be able to install an accessory that can trick other wires into doing double-duty in order to free up a spare wire to act as C.

Re: Nest Gen 3 turns off and back on within a few seconds

Engineer — Sun, 07 Aug 2022 18:11:39 GMT

Are you certain that your problems have been 100% resolved since you've added the C wire? Since I've added the C wire, I still get the compressor dropping out for a few seconds then coming back on, typically when the schedule drops down in temperature.

Re: Nest Gen 3 turns off and back on within a few seconds

Ryan_G — Thu, 18 Aug 2022 13:40:12 GMT

Hi everyone,

Thanks for staying with us here in the Google Nest Community.

Based on the response of other members in this post, it looks like the issue has been resolved by connecting a C (common) wire to their unit. There are system that can provide stable power to the Nest Thermostat even without a C wire, however, there are instances your Nest Thermostat would require a C wire like it is unable to connect to the Wi-Fi and function properly as the power fluctuates.

Thanks for sharing your thoughts here TROBBS and wyounger.

Regards,

Ryan