HVAC system has three integral parts-Ventilation, Home heating, and Cooling. The V in heating and cooling or ventilation means the system works by trading air in a closed area with the air in the atmosphere. However, a/c system does a great deal more. it eliminates the unpleasant scents, extreme moisture, replenishes the oxygen, control temperature level, discards of air-borne germs, warm, dirt various other harmful things.