Actually, sleeping on a cold floor or unprotected in cold weather might give you pneumonia. AC or a fan never, they are too weak.
I used to sleep with windows fully open in winter (that’s the way I like it!) and one morning I woke up with my blanket on the floor, my back completely cold and blood everywhere (from nose). I almost died from that pneumonia as doctors told me later. My body was cooled to the point, where it no longer was able to fight bacteria inside my lungs, so they had enough time to multiply and attack my body.
But AC or a fan are weak, I have it on all the time.
Yes, viruses and bacteria cause colds, but when you’re healthy you often don’t even notice you’re sick.
Those who made those tests I’m sure didn’t cool their test group to the point where they could die.
Pneumonia is probably caused by bacteria that we already have in our lungs and the way you make yourself sick is by cooling yourself to the point where your body is so weak that it will allow those bacteria to breed.
For the unbelievers, there was a story on the news maybe 5 years ago, where half of soldiers in baracks got pneumonia, because it was unbelievably cold inside. Even if they all were infected with some kind of bacteria, there is no way half of them would become sick if their immune system were intact.
So, COLD WEATHER/CONDITIONS MAKE YOU SICK indirectly. Grandmas are right after all.