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Are Nest Thermostats Killing Air Conditioners?

The Nest Thermostat is a beautiful product. The little LCD and metal hockey puck made consumers suddenly care about how cool their thermostat looked. The advanced features gave us the first palpable look into a connected home. We didn't roll our eyes and Google noticed. But before you stick the gold stars on your Dieter Rams poster and Google's new puck to your walls you should make sure it won't kill your HVAC system.

My house is 10 years old and we moved in just over a year ago. We had a new AC installed at our house last year and put a Nest on the system a few months later at Christmas. For some reason the air conditioner would turn on all the time even when set to off or heat. Since it was a brand new, and extremely quiet AC, I didn't notice that for a couple of days. I double checked the wiring and setup and was fine. I fought it for a while and it eventually it turned off. It seemed to work fine for the rest of the winter months but the thermostat displayed at warmer temperature than any other thermometer in the house. I dismissed it as a merely a better temperature sensor in the $250 Nest than the $8 meat thermometer in front of it. Once spring decided to show up and the Nest clicked on the AC, I discovered that my brand new AC was completely seized and needed to be replaced.


After electricians and HVAC technician visits with lots of head scratching, I started Googling. It appears there is a design flaw in the Nest Thermostat's base. Nest decided to use Field Effect Transistors (FETs) in the base to control the equipment as opposed to the traditional relays used by other thermostats. Imagine the FET as a switch and instead of flipping it with your finger the switch is flipped from a control signal. But these FETs and base stations are shorting out, effectively leaving the switch in the 'On' position. In my case, this triggered the compressor but not the system fan (very bad.)

I'm not the first to notice this. There are a number of consumers and technicians (Nest Forums, HVAC forums, Amazon reviews, Business Insider, etc.) that are reporting their thermostats showing hotter temperatures, shorting out, and constantly running equipment, rapidly cycling or running ACs all the time, even when the thermostat is set to off and even in the winter. Beyond damaging equipment, this presents some serious safety issues.


When I spoke with Nest customer service they were polite and immediately said, it sounded like I had a "bad FET in the base." I asked if this happens often, and the rep said, "they do see this happen." I asked if he'd seen any that ruined ACs, and he said, "not usually." I was sent a new baseplate in the mail, but I don't think I'm going to hook that up.

To be clear, I love the idea of Nest. Take something overlooked and ignored like the lowly thermostat and redesign it into a sleek and exciting product. As Nest and Google continue to reimagine the everyday they need to remember to keep the fundamentals of engineering ahead of the principles of design.

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