“Alexa, why is it so hot in here?”
“Because the Nest is a moron and didn’t send a signal to the AC.”
“Thanks, Alexa! You’re the best, but it’s time to fire Nest.”
Okay, that’s not how it went down, but after a month of catching the Nest at not starting the AC, the wife got hot under the collar and it had to go. Here’s the details for those who care about such things.
The Symptom
At random times, we’d notice it was hotter in the room than our comfortable 70 degrees. Especially at night, when waking up in a pool of our own sweat not induced by gymnastics or haunting dreams meant the AC wasn’t running. I could set the Nest to Off and then Cool again and it would start a timer before activating the AC. That worked most of the time.
The Troubleshoot
I contacted Nest via chat and they looked at voltage numbers and my wiring and saw I had a 4-wire system. That meant only 4 wires ran from the air handler in the attic to the thermostat. That’s a wire for power, fan, AC and heating. Nest is very proud of their patent that enables trickle charging their thermostat off the line while the AC is running. The problem is that shaves off a few volts that the AC might need to start. Nest offered to send a tech out from a local AC company to run a fifth wire for free. That’s very nice, because that wire and labor isn’t free.
The Appointment
The AC tech called to come over that evening rather than the scheduled appointment. On arrival, he thinks the 4 wire is fine, but the base is bad. He also trimmed the wires because they were longer than they needed to be. He called Nest, gets put on hold forever and eventually gives up, and says he’ll be back for the appointment. Then the case is closed as completed.
The Internet
Turns out, the internet has known about the 4-wire concern for sometime. One AC guy even made a video, that says your fan will automatically turn on with the AC, so move the wire intended for fan to the Common wire position (the fifth wire) in the attic and at the base of the thermostat and it’ll be fine. That didn’t work on my Trane. Outside, the AC came on, the fan did not.
The Solution
The wire wanted to fire the Nest since the get go, so the day after the case was closed, I swapped it out for a dumb thermostat. Which I had to make an extension jumper for because the AC guy trimmed them so one of them wouldn't reach. Never shorten the wires for a thermostat, who knows what the next model will need and it’s not simple to get more.
Where are we now?
I’ve got a Nest sitting in a pile in my office. I have no idea if the base is bad or I just need a fifth wire run. And I have to mess with the dumb thermostat twice a day to shift from night to day mode. But the wife is happy.