Your HVAC system is one of the most expensive appliances in your house. When it breaks down, it can easily cost hundreds of dollars to fix — or thousands to replace. But those systems are mechanically-robust, and more often than not the failure is the result of the electronic control board breaking. However, ordering a new one from the manufacturer can still be pricey, which is why you might want to follow Wiggum_guy’s tutorial and fix it yourself with an ESP32.
Wiggum_guy lives in Minnesota, and so his home has a LifeBreath 155Max HRV (Heat Recovery Ventilator). Unfortunately, the control board fried and a replacement was $200. So, he decided to fix it himself with an ESP32 development board, and even added some additional functionality along the way. Because the spring and fall in Minnesota is cool and dry, Wiggum_Guy wanted to use the system as an air economizer, which simply pulls in the cool air from outside, circulates it through the house, and pushes the warm air back out.
To do that, he paired the ESP32 development board with a set of temperature sensors (one for inside, one for outside) and a solid-state relay. There is also a step down power supply and voltage regulator, and an OLED display and rotary encoder for control. Connecting the ESP32 in place of the original control board will vary depending on you HVAC setup and model, but Wiggum_guy has provided his schematics and code on GitHub. The functions on the ESP32 are controlled through the Blynk app and IoT service. The result is an affordable repair that is actually an improvement over the original.