Howdy yall, my 01 cummins defrost doesn't seem to work very well.
It blows good out of the drivers side 2 vents, but the passenger side 2 vents only blow very minimal air.
I noticed this yesterday driving when my defrost was on full blast and the passenger side window was fogging up and the drivers side was fine, and it was only 70 degrees and raining.
The tips are very appreciated

 

Probably a blockage somewhere upstream.... Maybe rent one of the camera's on a stick type things, and have a look down there.

 

Borescope, Check out ebay for a Depstech one. Good quality has a light and can fit in small places. Bluetooth to your phone but they have other models. I have a duel camera one and it's definitely something to keep in your tool box.