Bella Vista is a central, well-established neighborhood. Within a few blocks there are apartment buildings, medical offices and clinics, offices, restaurants and stores built in different eras, and that mix carries over to the air conditioning: recent units sit next to systems that have been running for years. It is about 5 km by road from the Climatiza office, in an approximate calculation.
In the older buildings the ductwork already has a long service life, and a duct holds on to part of the dust the air carries. Between the ambient humidity and the condensation of the unit, that dust turns damp and can feed biofilm, and it almost never gets to dry. That is why the first step is to learn what system each building has.
Data point: In an air system that looked clean to the naked eye, 10⁵ to 10⁶ viable bacteria per cm² were counted on the coil fins (Hugenholtz and Fuerst, 1992). It is a case measured in a single system, not a general figure, which is why the camera looks inside before deciding.