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Neither my 88 (gone) or 95 have such a beast. You may have to clean out ducts, air intake under wipers, or have a leak into cowl area. Try washing out cowl and ensuring the area drains clear thru botom drains in rear of fenders. Good luck.
I was referring to the grille area in front of the windshield, although it could be filled with dust not visible thru the grille and cause some overflow into the vent system. I think you can pop out the vent fittings in the dash and hand clean some of the vent/ac lines into the cab and that might help some.