Cold buses

Why are buses always so cold in winter, with drivers switching on the cold aircon? And all the windows always open, even whe it is freezing outside? It is particularly bad on the new hybrid buses, like route 40. Old people like me would like a bit of warmth on a bus in winter, the way things are it is difficult to heat our homes already, the old routemaster used to be quite warm in winter and cool in summer as you could open the windows at the top and proper fresh air would circulate. I feel sick now when I go on a bus and this nasty cold aircon is cisrculating, I have to get of and get try to get on an older bus.