Why do you need to change the air filters for your HVAC system? The purpose of the air filter is to help prevent dust, lint, pet hair and other debris from getting into the system. Dust and debris will eventually cause moving parts of an Air Conditioner, such as fan motors and valves to fail. When airflow is restricted, it creates a strain on the system and your AC unit will begin to fail.
The typical life span of a HVAC unit is 12-15 years, depending on the make/model, type, etc. This system was less than 2 years old and the filter had probably never been changed. Not only was the filter clogged, there was heavy dust and debris inside the coils behind the filter. This AC was working extremely and unnecessarily hard.
Changing your filters every 90 days is recommended if you don't have pets. If you have pets, especially multiple pets/pets that shed, changing your filters every month is absolutely necessary. Also getting your HVAC system serviced, by a qualified contractor, at least once per year is also recommended to keep your system running as efficiently as possible.