Bonneville blower has obstruction

I have a 1990 Bonneville. When my parents first bought the car the AC/heater blower would move large amounts of air. A few years ago the volume of air dropped and you can have the blower set on high and very little air will come through the defrost, vents or the floor. I inherited the car and have replaced the blower motor and fan and still the air volume is very low. Is there a filter (like a furnace filter) that could be plugged? Or a baffel that is stuck/ Any ideas/guesses would be appreciated.

More than likely what has happened is the evaporator core has leaked and the fins are clogged. I have seen this a number of times. When the evaporator core leaks, dust and other particles accumulate on the fins and prevent air flow.

Remove the blower motor,look inside of the case and you should be able to see the clogged evaporator. Clean out the fins and you should have air flow again.