An HVAC system consists of your furnace, your air conditioner, and the blower motor inside the furnace is also part of the HVAC system.
HVAC simply stands for heating, ventilating and air conditioning, and part of its job is to maintain the temperature inside of your house for you whether it be summertime or wintertime. This also includes the indoor air quality, which is controlled by the blower motor inside of the furnace and air filters that you have inside the system. Using this, it can improve the indoor quality inside of your house.