on the buses i used to drive we have a double ac system with 2 separate pumps and 2 separate systems, one for the front and one for back of the bus
or, in other cases, one for the lower deck and one for the upper deck

so it was quite easy to be travelling along in cold bliss while some of the punters were sweltering

so you've got to have a larger capacity for everything vs a car system which is only going to have something like 700g worth of refrigerant in it against the 11000g in the coach system which is possibly why you have come to that conclusion