Something that I believe should be brought up is the colour of the vehicle itself, obviously darker colours, basically, absorb more heat than lighter ones and it definitely shows in hot conditions, at least where I live.
On one hand, there are bright blue 200MMCs (no air-conditioning however equipped with tinted windows) and for the most part, the driver and passengers can cope with the heat.
And on the other hand, there are black Volvo B7 Eclipse Urbans (with functioning air-conditioning but no tinted window) and said AC had almost no effect whatsoever. On one occasion, during the heatwave period, I boarded one of these black Volvos which very soon decided to break down. The exterior body panels were scorching hot upon making contact with them and I later found out it failed due to overheating. Had that bus been (let's say) white, a whole breakdown may have been prevented