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

[Engineer]

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.

[WorkPlayDrive]

FIXED: Here is an update on my situation

Original Issue:  I've had a Nest thermostat since the 1st gen pre-release running without a C-wire and had no issues with 1st gen and now my 3rd gen until the May 2022 update, where my AC started turning off and then immediately back on again.  It happened daily, and on occasion, my condenser would not kick back on causing my AC to run endlessly when I'm not home, heating up the house with hot attic air.  

My Wiring:  My central AC only has one zone and is connected to the 1st-floor nest along with my zone 1 baseboard heating.  I have separate heating and cooling systems with the following wires connected.   Y1, G, Rc, W1 and RH.

THE FIX: Normally, I do my own wiring, but I called a tech from a Nest installation HVAC company because my installation type was not covered in the instructions, and if this failed I wanted to ensure it was installed correctly.  He connected the Nest Power Connector to my AC unit and it's been fine since.  We also tested the Zone 1 heating and that worked fine as well.   

Important Note: During the process, my Nest battery dipped below 3.6, which turns off Wi-Fi until it achieves a 3.8volt battery charge.  I have an older 3rd gen, and my battery never goes higher than 3.74. Even after 24 hours would not charge above the required 3.8, so I pulled it off the wall for 20 minutes and charged it via USB.  It connected and has been functioning fine for the last 2 weeks.   

[arjan1071]

We noticed the short cycle issue about 3 months ago in our upstairs unit. We assumed there was something wrong with the HVAC system. Starting today, the downstairs system started to short cycle, probably every 5-10 minutes.

In case it helps someone figure this out, here's the data from our experience...

- we have had both Nest thermostats installed for at least 3 years, perhaps 5 years now (I forget).

- never had this problem before.

- I checked the downstairs system. No C-wire. I assume upstairs is wired the same. However, given the systems have worked fine for years, this should not be related to the wiring, which has not changed.

- Moments ago, I deleted everything we had on the Schedule via the mobile app. I then went to settings and turned OFF every feature (Auto-Schedule, Early-On, Cool to Dry, Sunblock, Airwave).

- neither system (downstairs nor upstairs) has short cycled since I turned everything OFF. (Of course, it's only been 45 minutes but it was short cycling more frequently before these changes).

- Also, when it did short cycle, it was only the blower that was shutting off, not the compressor. The mobile app showed the compressor as running (blue background on the screen) and I ran outside to verify that the compressor was running (it was) while staying on the phone with my wife inside, who confirmed that the blower was still OFF inside. I'm not an HVAC tech, but I'm guessing this isn't a good combination either (compressor running within the blower). I understand from reading the entire thread above that most people were talking about their compressors short cycling... which was not the case for us.

- Interesting point... In every short-cycle case, if I walked up to the thermostat (to activate it), or if I opened the mobile app and changed the temp, the blower came back on (exactly 4 seconds later... every time). I tried this at least a dozen times (over two days), carefully spacing my timing when I approached the thermostat to be purposefully inconsistent. In every case, the blower came back on in exactly 4 seconds from thermostat activation.

- this led me to think that perhaps the Nest had a software bug, that it thinks no one is home (Home Away activating). When I walk in front of it, activating the screen, it realizes that someone is in fact home, and comes back on. But again, this is only for the blower.

- I'm not an expert in this domain, but all evidence from my experiments at the house (with two Nests, both behaving strangely, but in the same strange way), suggests that this is a software bug introduced in a recent update, perhaps in late Spring or early Summer 2023 for us. I understand others experienced the issue, starting in May 2022.

I hope this helps... and even as I have taken considerable time to type this, we have experienced zero short cycles whereas it was every 5 minutes or so just before I turned OFF all the features.

[arjan1071]

^Update... system still seems fixed with all Nest features turned OFF.

[jmatthew]

We have had Nest Thermostats and Smoke/Co2 detectors for several years and are generally happy with them.  However, the Thermostat on our main level has begun to short cycle our A/C.  While running, it will turn off for about 5 seconds and then restart the A/C unit.  This began last summer.  It does not seem to do this in Heat Mode.  I disabled our Home Away Assist, thinking our phones were the problem because we live in an area with poor phone reception which is on again and off again.  However, that did not solve the problem.  Nothing else has changed that I can think of and this seems to be a newly developing issue with our thermostat.  Needless to say, I am concerned about what it is doing to the compressor to stop and restart on such a short cycle.  Seems like a new thermostat would fix it, especially after reading previous comments about the same problem.  

Will Nest stand behind their product?

[Heartless]

I seriously doubt they will stand behind their product since I've had the same problem and they told me it was a C wire issue.  Plenty of others have C wires and the same issue, so it looks like their software update is to blame.  Looks like the ecobee thermostat is the solution.

[dpalmer79]

No they won't.

I suggest getting a Honeywell or try the Ecobee. Your nest could ruin your compressor. 

[Heartless]

Nest told me I needed a C wire after all these years, so I'll probably just buy two Ecobees and call it a day.  Too many others are reporting the same issue and they have C wires.

[jmatthew]

Yes, mine have had the C wire hooked up since the start.  Unless there's a problem with the 24v transformer (that supplies the power for the thermostat) going on and off all of a sudden, I would think it's the Thermostat.  I'd be surprised if it was the transformer since they usually just fail and stay broken. 

[chase314]

I ended up getting an Ecobee Premium for ~$125 through my electricity provider. So far no issues! Too bad, I hadn't had any issues with my Nest for years but I'm not about to risk my brand new HVAC over this. 

[Ronstang]

OMG!  It is not a C wire issue people. read the thread....it's a software issue.  If you have added a C wire and think you have solved the issue....you HAVE NOT.  Now, there may be different degrees of this issue as some report the short cycling happens all the time or a lot whereas mine has never been that way an may only happen a few times a day.  I have been able to minimize the issue by turning EVERY feature of this useless thermostat off, but it still happens occasionally.  So, if adding a C wire means you have not heard it happen then stay in your house and stay awake until it happens again....because it will.  

There is no way this can be a C wire issue.  My thermostat worked perfect with NO C wire for many many years and only started this absurd behavior after the last software update last year.  

The only thing I can think of is with an old battery maybe it is not staying charged enough and somehow there is a conflict with this and the new software....but I am not willing at this point to spend another dime trying to fix Google's problem when they won't even admit they have one.  If I spend any money it will be on a different brand thermostat

[sherpa]

The same issue started for us in spring 2023. It may have already began in 2022 but we didn't notice. It's been going on for months and today finally had an HVAC specialist come and tell me it was the air filter. Air filter has been removed and the problem persists. I chatted with nest/google support and they are just telling me it's because of the air filter which obviously is not the case. I mentioned that the problem likely began with the most recent firmware update. I'll most likely re-install my old thermostat. This nest has been running well since early 2019. C-wire is installed and battery voltage is over 3.7 V. 

[dolphindreams]

I'm having this same problem on my Nest installed at my apartment and unfortunately I don't have the luxury of installing a C wire just to make it work.  I think I'm going to switch it to a different brand as others in this thread has stated because I don't want this to short circuit my blower.

[Homehandy]

Alright, I experienced a recent issue with my Nest that had functioned well for 3 years. 6 months ago, it started losing battery, low power, etc... I'd charge it and put it back on because I didnt have a C wire attached at panel yet and wanted to see if it fixed it. Short term yes. Long term, got worse. Fast forward, unit starts to die. I wired, per spec a C wire (blue) to the Nest wire base. This fixed the low power.

However, this is where things turn from bad to awful. I had power now, but something in the firmware is wrong. My A/C unit was short cycling badly and not running. Kick on, off immediately 2x in a row, then turn on for 5-10 seconds before turning off completely. This is horrible for a ac unit so I turned off and decided to fight again next day. I decided before diving into the AC unit to check for contactor/capacitor/fan motor issues, Id install a Ecobee premium to see if it fixed issue. Swapped wires over and immediately ran AC.

This is not a great look for Google. They are failing to support their firmware to the point where it will damage very expensive home equipment.

Tldr - Nest use to be great, now a dangerous home device. Use at your own risk or get any other thermostat.

[Engineer]

Lots of threads and posts on here regarding how Google screwed up the software. The only fix I found is to replace the thermostat with another brand.

[dpalmer79]

Bingo. 

[Markjosephp]

Hello everyone,

I know it has been a while, and I see some of you shared some input on how the C wire and a Nest Power Connector helped the Nest Thermostat stabilize its power.

A power-related issue is one of the main reasons why HVAC systems have short cycles. It's either insufficient power that causes other wires to be energized in order to sustain the needs of the one who's active but still isn't enough to maintain, or a specific wire or terminal is faulty. It sounds complex, as others have C wires but are still experiencing the same issue. Please don't give up on us yet; I'd be happy to take a look at this.

Can you share with us a photo of your thermostat's wiring and its power readings in the Technical Info or in the Equipment Settings? The settings may vary depending on the Nest Thermostat versions you have.

Regards,

Mark

[Engineer]

Hi Mark! I see by your title you are a community specialist. Are you also a product specialist? There are multiple threads regarding this issue and the questions you've asked have already been answered. You will need to invest a few hours time as there are so many posts with pictures. To save you some time, there was a software change over a year ago that caused this issue. It appears that nobody from the Nest product team has read any of these threads. I suspect you are a contractor and do not work directly for Nest and have no wherewithal to elevate this issue. After you have had a chance to review all of the posts and threads on this topic, may I ask you to explain the software situation to someone at Nest And how it has nothing to do with the C wire?