Another critical part to the system Filters. Different Systems require different filters to remove Large and small particles from the incoming air.The filter selection is dependant on the final requirements of the air quality used within the building. This also prevents the debris from the external air penetrating the system and clogging up either heating or cooling coils. This will reduce the efficiency of the system and eventually either overheat or burn out causing untold damage.
Dampers are the next point. These can be either manually altered or in a lot of cases set with automatic controls to vary the air flow or shut the air off totally when the AHU shuts down. Then there are Fire Dampers in systems as well. Failure of any part of this system is going to be costly. Maintenance of such systems is essential at all times.