Two of my cars sit outside under a tree which sheds seeds and leaves at various times in the year. I have had to replace two evaporators at great cost because of crud that is sucked up into the ventilating system and ends up against the evap, corroding it over time. It is almost impossible to remove all of it by vacuuming through a hole in the plenum.
So I bought some fiberglass window screen, cut it to fit the cowl vent, removed the cowl and inserted it between the metal screen and the cowl. I put new butyl tape on the sides of the metal screen since the old tape was dried out, then I used small zip ties to secure it almost invisibly to the cowl cutouts. I vacuumed out the chamber beneath where the wiper motor and air intake is located and replaced the cowl. The whole thing took an hour and should once and for all time keep crud from working its way through the metal screen into the air intake.
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