Usually, in many HVAC systems, there is an indoor and outdoor part, where the outer part is a big box that is bigger than the inner part. Many people believe that in this large box the fresh air from the outdoors is ventilated and brought into the house, but what is the reality? If so, this issue can be a concern on days when the air outside is polluted and full of dust. Many air conditioners do not draw air from outdoors. In the following, we will explain the operation of the air conditioner and how they bring cold air into the house.