Arrived to perform an ac tune up on a Mini-Split system. Cycled system on customer said he hasn’t changed the filter since it was installed. Airflow even throughout the house. Climbed into attic. System has a merv 11 16x25x5 inspected condition was completely hammered. Heavy with debris, reducing system efficiency and lowering indoor air quality due to more dust cycling thru the system. Customer upgraded to merv 16 16x25x5. Outside condenser, heavy debris in the coils. Sprayed chemicals inside and out. Washed completely down inside and out. Checked electrical components all within range. Refrigerant pressures are good. Cycled system off and on. System is operational upon departure. Merv 16 filter must be replaced 8-12 months. More can cause system suffocation and begin loosing system efficiency, longer run times to get to desired temperatures, and cause more wear and tear on system.