Some what confused on my duct work

[Wax-um]

Anyone have a diagram for the duct work for an 82 MCI 9. Im getting ready for a new floor and dont want to block off anything I need. The front ducts blow cold but the rear ducts do nothing. I read that MCI had an optional rear airsetup that I dont have. Maybe my rear duct work is not used maybe it has been blocked off or is a cold air return that isnt moving much air. I do have aftermarket rear aux air but its independent and doesnt use any duct work. Its possible they blocked of the rear ducts when they installed the rear air.

I would also like to clean the duct as good as I possiby can without removing original floor any tips on cleaning would be appreciated too.

[gumpy]

There are 4 return air vents on each side. 2 in front, 2 in the rear. These are connected to the return air tunnel via 4" plastic tubing.

There are diverters in the stainless duct to separate the return air from the supply. All the supply goes up the inside of the
false wall and vents just below the windows.

[James77MCI8]

The MCI supply and returns share a common plenum that runs down both sides of the coach. The duct gets "split" just past the mid point of the coach. At that point the lower half becomes a return and the upper half remains a supply. The two front ducts as you are referring to are the supplys and the the returns are the two located at the rear of the coach. You can verify this by firing up the A/C. The front will be blowing air out and the rear will be pulling air in.