Controlling Dumb Air Conditioners with a Nest Thermostat

I've been using wireless ESP-8266s to control our portable air conditioners for a few years now. I decided to finally integrate them into the thermostat controls, rather than using voice commands or clunky timers.

Here's the previous post about setting up the ESP-8266s. This year, I'm going a step further, and designed and 3D-printed a case for the electronics:

Tying the portable air conditioners into the Nest Thermostat required a Rube Goldberg approach:

I initially tried wiring the Nest Thermostat to a resistor as a dummy load, so I could use software to see when the Nest was in cooling mode, and send a command to the portable ACs to turn on. But the Nest Thermostat didn't recognize the dummy load as legitimate at any of the resistor values I tried. However, it did recognize a relay I had puchased to turn on a humidifier.

So I used the relay to turn on a night light, and used a zwave "indicator light sensor" to detect when the night light was turned on (and thus when the Nest Thermostat was in cooling mode).

From there, I could use my smart home hub to turn the portable AC's on and off according ot the cooling status of the Nest Thermostat. Woohoo!

Update October 2020: I had to wrap my nice 3D-printed electronics cases in duct tape against the AC unit to keep my 3-year-old from stealing them, but otherwise this system worked really well this cooling season. I'm very pleased!