95 C1500 window defrost problem

Hi
I have a 95 C1500 with the 5L engine.
When I turn the defrost on the passenger side has a good air flow and clears very quick, however I have a very weak airflow to the driver side window and takes over 15 minutes to clear.

I looked at a schematic and it looks like there is no door or gate that would direct the air between the two sides.

I am looking for help to figure out where to start without taking the dash apart.
Thanks

Must be something stuck in defrost duct- get an air hose, and blow out the ducts- maybe what is in there will dislodge and finally come out in pieces- pencils will fall in them- and other dash debris..