Re: What does SMB do........
My 2008 E-350 cargo van has the factory rear A/C- Heater unit without a headliner. It had a distribution cap that replaces the duct that goes up to the ceiling on vans with ceiling vents. It seems to distribute the air nicely throughout the back of the van although it is a bit colder in the left rear where it comes out than in the rest of the van. The part number for the duct is F2UH-19A869
Also from what I can remember the duct that goes up to the ceiling on vans with a headliner just dumps into the headliner at the left rear. That system works great and will be hard to replicate with a pop top no matter what. Remember that cold air drops so getting it up near the roof will always make it work better. It may take some experimenting and time to get something close. In homes and building they always have a trunk that is large and then it steps down more and more as it goes to the outlets. Building something like that on your van may work almost as well as the stock system. The stock roof vent system has a large duct up to the ceiling and then a large gap between the ceiling and the headliner for the air to move freely. If you have a bunch of passengers in the back that additional heat they put out also comes into play, if you just want the back to cool almost anything will do that but evenly is another story.
Just for more information the rear A/C-Heat unit is a recirculating system meaning it does not get fresh air from the outside it only recirculates the air inside the van. The only fresh air it gets is from the front A/C as long as its not on Max.
Lastly the amount of air volume that comes out of the rear Heat-A/C unit is quite high so any ducting that you might want to use should be large (very close to the stock size) and free flowing as to not restrict the air movement. Without proper air movement the rear evaporator can freeze up on a hot day and that can prevent the Freon from moving correctly in the whole system. It is also hard on the fan motor.
Joey2cool... some vans have this rear A/C-Heat prep package.This is from my 2008 order guide;
57X Auxiliary Heater - A/C Connector Package w/Rear A/C Controls - $110
Aux heater-A/C connectors; Rear A/C controls in instrument panel
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2008 Ford E-350 V-10 EB
Transformer Interior
U-Joint Off Road 4x4 kit in the garage
2004 F-350 Dana 60
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