Good thought. Appreciate all the ideas. The vent fan definitely adjusts on auto though. Usually it hovers at around 9 out of 11 then lowers a couple as it approaches (but almost never reaches) set temperature. In fact, my wife frequently takes it off of AUTO and lowers the fan speed - understandably because if the car doesn't cool down much anyway, why bother having the fan blasting loudly?The AC in our 2018 Model 3 (blue with white interior) was occasionally failing to cool the car properly, when set on Auto. It wasn't increasing the fan speed as much as necessary. I live in south FL. I had the car serviced, and they replaced a control unit (low voltage controller, left), which resolved the issue, under warranty.
I'll add that the AC does work. It can bring the temperature lower than the outside temperature. It also can reduce humidity in the cabin to help defog the windshield. How well it works? Well... not very well.
Anyway, hopefully they can figure out what's wrong next time. The service center said they will have to schedule fixing it on another service visit so I'm going to pick up my car today.