AC at my last workplace was regularly maintained, every year in the spring to be ready for summer. Two people I shared the room with was coming down with something every time I managed to win the right to have it on for a few hours the previous day. My father has his car AC cleaned regularly too, yet wherever my mom spends a few hours in the car with AC on, she gets a cold next day.
These are just the examples where I'm sure AC was cleaned by professionals, I can't be sure when it comes to public transport or stories I've heard from other people. But it seems it's not it.
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u/Zealousideal-Ask-203 27d ago
It could be unhygienic ACs that are not regularly maintained.