I just watched 12 Angry Men (1957) again for the third or fourth time. About halfway through the movie the fan is turned on and it starts pouring rain outside the open windows. The fan and the rain create quite a bit of distracting noise for the second half or third of the movie. I racked my brain trying to understanding the significance of that from the filmmaker's perspective. Something so blatantly attention-getting as that much noise, very noticeable and obviously deliberate in the movie, must have a purpose. Increased tension? Some kind of metaphor? A psychological ploy?
So, what is the purpose of the noisy fan and rain through so much of the movie?
The fan and heat represent the frustration of the jury to not come to an immediate decision. The fan finally gets fixed when the jury breaks their tie, giving the room and the viewers a small sense of relief. The rain represents the storm that erupts inside the jury room, where members literally attack each other over their conclusions. If you recall, at the very end, once a decision is reached, one juror remarks about how the rain has stopped. The storm, both outside and inside, is over.