Ac preventative maintenance on a gas system from 2021 with an air filter 20*20*1. Upon arrival the customer showed me around the house and brought to my attention that there was some kind of biological growth in some of the vents. He also stated that he changes the air filter whenever he sees it to be dirty. During my inspection I conducted an air quality test, checked electrical connections and components, and inspected the ductwork for dirt buildup and to see how far along that growth has travelled through the system. The air quality test showed there to be a lot of particulate matter in the air as well as carbon dioxide and chemicals. The ductwork was very dirty and there was more growth through out the ductwork and plenum boxes. I showed videos and pictures to the customer of what the inside of their system looks like and they decided to get this issue resolved because they have a newborn with weak lungs and want her to come home to great quality air. The customer wants a full