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jack b
Gone Fishing
Cape Cod
reply to PSWired

Re: New Nest Thermostat- 2 stage

said by PSWired:

Almost all residential thermostats have control over the refrigeration and air circulation functions separately. That's how the "fan on/auto" function works.

Yes they do, most have a system FAN ON manual override switch and all that does is supplies 24volts to terminal G continuously.

Typically terminals Y (compressor) and G (fan) are energized simultaneously on a cooling call, and the bug that must be happening with the firmware update is that terminal G is NOT being energized, therefore the blower will not run.
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Cincinnati, OH
Nest sent someone out to the place to check it out. I didn't hear back directly from the person I talked to, but when I called in later a level one person told me that notes in the case showed that the green wire had fallen off. I give them kudos for sending someone out on their nickle, but I'm not so sure I buy the idea that the green wire just happened to fall off at the exact time a firmware update went out.

From examining the web page that shows energy usage I found that I could pinpoint the exact moment the thermostat rebooted after the firmware update (because the thermostat after a reboot shows the temperature being set to the value it had prior to the reboot, as if I had changed it on the web page, but I hadn't changed it at that time), and from then on until the service tech got there the thermostat was trying to run the A/C all the time.

I'm still in the dark as to exactly what happened. What this does show though is that there is a great need for Nest to give customers the ability to opt out of automatic firmware updates, especially for thermostats in vacation homes and other places where there is no human being present to verify that things are working correctly after the update. There should be a way through the web page to turn off updates and then turn them back on once you are there to watch what happens afterward. As I posted earlier, if I didn't have other temperature sensors in the place that started emailing me, I would have never known that this was happening.