How should a coach driver manage the cabin heating, ventilation, and air conditioning (HVAC / Klimaanlage) for passenger health and comfort?

1. Keep the heating on maximum (35°C) with all vents closed
2. Cool the cabin to freezing temperature (5°C) in winter
3. Turn off the ventilation completely to save fuel
4. Set a reasonable passenger-comfort temperature, maintain adequate fresh-air circulation, keep the windscreen clear, and adjust the system for occupancy and weather