In our home, the air conditioner(Air con.) has a air filter which we get it cleaned regularly so that the cooling coil(evaporator) remain clean, efficient cooling and remains germ free. In our cars it takes only 30 days for the car's cooling coil(evaporator) to get dirty.
As soon as you buy a new car or in your present car, get a air con.cabin/pollen filter to increase the cooling efficiency. Clean cooling coils will eventually bring down the petrol/diesel oil consumption.