1996 Avalon Center dash A/C Vents

My '96 Avalon has very little air coming out of the center dash vents with A/C on high. When I close the driver and passenger vents near the doors, it pushes a little more air, but nothing like the two outer vents. This has only been over the last couple of years - could the ducting to those center vents become disconnected or could something now be blocking them? What can I do to resolve the issue? I was going to remove the dash, but can't even get the glove box out (plus I am concerned I might set off the passenger air bag). I found two screws in the glove box, two bolts under the passenger dash panel, one nut holding the electrical cover on the lower passenger floor board, but don't see any others. Any ideas or help would be greatly appreciated.

I found something in a radio installation manual telling me to remove the center bezel after removing the temp control knobs and the two screws holding the bezel in place. There are about 4 or 5 clips keeping it in place after removing the screws so I started near the ignition and pulled straight out. After the bezel was removed, I reached my hand through the cener ducts and way back in there I could feel a flapper door kind of like a very thin light duty shiny-spongey scouring pad. I turned the key on, placed the air diverting switch into each one of the settings and found (in clockwise order) air would divert to each location. Two of the settings, feet/defroster and defroster caused the air to flow up to the flapper that I could reach through the vents. At no time did the flapper door move as I set the switch to each of the settings - I think this is where the problem lies. I'll post more if I can get to the source control for this flapper door.

I asked a friend to check it out - he thought maybe a tissue or leaves may have been sucked up in to the ducting and might be blocking the vent. He blocked off al the vents and shot 120 psi compressed air through the vents but all that came out was a little dust. He suggested slicing into the spongy material since this is not a moveable dam/door. He did and viola, more air is now coming out of the center vents. He also evacuated and pumped down the system to check for leaks, and removed all the old A/C oil. I guess factories don't always pump out the moisture in the system and some stays in the oil. The new oil is a synthetic specificly for 134a, but he forgot to account for how much oil he put in and overcharged it with 134a, although he weighed how much he put in as per the underhood sticker, which doesn't indicate anywhere how much oil to use. After it started to rapidly cycle the compressor driving back to his house, he put the guages back on, evacuated some oil and freon, recharged it as per pressure check rather than weighing it, now it's 42 degrees at the vent (center vent mind you with the increased air flow) while idling. I'm telling you, it gets to 40 degress on 105 degree days and that's just while doing 30 - 45 MPH around town in heavy traffic:). My arms and face get so cold I have to redirect the air flow away from me.