The Svara of Reb Moshe that you can run a factory is not original. The Gemara refers to this as Avsha Milsa. This is not Maris Ayin. It is Zilzul Shabbos due to the fact that an overt Melacha is happening. We don’t care about Shvisas Keilim but something that we see as a Melacha is Zilzul Shabbos.
Therefore, this situation can and did change regarding air conditioners. Having a timer run a drill is Zilzul but having a timer or thermostat run an air-conditioner is just as good as leaving it on.
This is why I said that you don’t even assume someone turned it on. I’m speaking about a weekday. The sound of an air conditioner going on is not anymore the sound of Melacha.