Moving air will cool you down, as long as you've got the movement of air on you - just like having a fan on. As the train moves, the windows probably help expel hot air more than taking air in - but when you're not moving, windows are next to useless. Air conditioning solves that, but it can't work when more and more hot air is coming in from an open window.
It's actually the opposite that causes a problem with our Cl317/7's.
The windows on these really should have been sealed shut when they were fitted with A/C, but they weren't. Consequently, folk get on and immediately start opening them (the eejits). Then, as the train goes along, lots of lovely cool air comes in through the windows and hits the thermostats. The train then thinks
"Hmm, it's a bit parky in here. I'll just put the heating on" irrespective of the actual ambient temperature. This then causes the temperature to rise and the punters to open more and more windows which just makes the problem worse.
I can usually guarantee that when a punter comes and complains that the train is too hot they will point to the carriage with all the windows open. I try and keep them shut as much as possible by going through the train at each terminus, but it's a thankless task because the punters just open them again. I've complained about it to Fleet as well, especially as the solution is actually very quick, simple and cheap (replace the hopper handles with metal clips), but nothing every seems to get done.
Quite frankly they do it to themselves. Let 'em fry.
O L Leigh