I think what you’re failing to understand is that newer HVAC units are designed to be run in a specific way. if you disregard that, and run it like a unit from the 1980s you will halve the life of the unit.
yes, most of the “brains” are on the unit itself but without proper “eyes” the brains are useless.
I’m not even an HVAC tech but I’ve worked on them enough to know it’s a dumb idea to just replace your thermostat with “a raspberry pi and a bunch of 24v relays”. there’s just too much risk of things to go terribly wrong and multiple people literally die.
I have smart thermostats. I block 100% of their traffic.
Why?
One winter I woke up to my house being not 70, but 50. BOTH of my units had stalled after a botched firmware update.
I can’t trust a multi-billion to fuck my house up while I sleep. not once, not twice.
now they are nice glowing thermostats I can see in the dark that my power company paid for.
couldn’t be happier since cutting them off.