Another poor airflow out the HVAC vents thread

[mlipmd]

I have a '90 ZR-1 which has developed a problem that I have researched on here and on the Corvette Forum and Googled and have yet to find a solution to, without ripping the whole interior of the car apart. I have cold AC, I have control over the vents (so I must have vacuum), I have control over the blower speed, but the airflow out of the vents is very poor. Setting the fan on "10" has the fan running at top speed but has the airflow I would expect out of "2". I have removed the blower motor and the evaporator is perfectly clean as is everything else I can see in there. I removed the blower motor controller to look into the other side of the evaporator and that area and as far as I can see is also clean in there. I attached a suction hose to my shop vac and sucked up in there as far as I could go, and nothing came out. I also put it up into the heater vents in the interior of the car and got nothing out. There must be a mouse or other rodent's nest in the ducts somewhere or total deterioration of the small amount of foam sealing the ducts, but where do I look next? Is there anyway to access the main duct system without removing everything under the passenger side dash, and if I did that, would I find where the problem is? I would hate to take that all apart and not find the problem.