Many vehicles made after 1990 have a cabin air filter in the AC/heater (HVAC) system. Have you ever wondered why? It’s not just to clean the incoming air as the name suggests.
A couple of things happened to vehicles in those years that made cabin filters a great feature. First cars got smaller and evaporators – the unit that cools the air – got smaller. Second, the industry refrigerant changed from R-12 or Freon to R-134a because of ozone depleting substance regulations.
Older, large evaporators had lots of space around the tubes and fins for moisture from the air to run through without freezing. Dust, pollen, bacteria that came into the car through the fresh air intake was washed out quickly by the freely running water. The smaller, more compact evaporators were redesigned to increase efficiency but they had little space for water flow. They also ran a bit warmer which didn’t pull as much moisture out of the air as before.
