Is it actual AC or swamp coolers/evaporative cooler? Usually as I mentioned elsewhere the licensing requirements (at least in the US) for actual AC systems usually involve a portion on computing heat load/etc in order to size a system.
Although, I'm betting the engineering side of the tram probably avoids needing anything other than the equivalent of the US PE/etc. Its probably a bit tricky because the needs of being able to load/unload people quickly also probably tend to dump a lot of hot air into the car. Either way though, busses, cars, trains all tend to do ok in hot climates because they have massively oversized AC systems and can move a lot of air relative to the enclosed space.
Returning to my original point, I'm betting your trams don't actually have AC, from your description I might guess they have some kind of evaporative cooler.
Above 30°C it's actually more comfortable to just ventilate the train instead of A/C.