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Discussion Starter #1 (Edited)
I've searched through LOTS of rear AC threads on here, but I have not found one about running duct from existing front AC to the rear. Has anyone tried this?

My thought is to connect duct to the passenger side floor ac vent and somehow run that to the rear. I've tested the concept with flexible duct, and it works quite well, but the crux is how to get it from the dash to the cargo space CLEANLY.

So far, the cleanest/simplest idea I can come up with is to come out the bottom of the dash on the passenger side, cross towards the rear staying close to the center side of the passenger seat frame without blocking the battery or fuel access, then drop over the cargo lip and go from there. Would probably need to use some sort of plastic pipe (PVC?) for this run and then build some sort of box around it to dress it up. Once to the cargo section, its much simpler and parts are available: https://nostalgicac.com/duct-hose-vents.html

Another option, which would give me my preferred end result of no visible duct runs, is to punch through the firewall into the engine bay and run some type of duct (PVC wrapped in insulation?) under the van and then punch back through into the cargo area. I'm just not sure I like cutting through the firewall, as well as how much the air will have warmed back up by the time it makes it to the rear.

Lets hear your thoughts/experiences!
 

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... for the sake of simplicity and in the almost as good category... I would tap into the pass. output as you suggest, run the (3"?) duct rearward, under the pass. seat and terminate it where the cargo floor starts...
 

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Air follows the path of least resistance.

I would guess you would have to plug up the remaining vents to get any meaningful airflow to the back of the van.
 

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Cooling works by removing heat, not adding cold.
A much more efficient way to remove the heat from the rear would be a simple fan to circulate the air in the entire van.
If you were to add a supply, you would also want a duct to pull the warmer return air back to the evaporator coil so it can remove the heat from it.
But it would be easier to simply run a fan.
 

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What wheel base and what are your cooling objectives? I have a 159" with open aisle to rear doors. By directing the dash vents and running with air exchange closed my mid-ships bed/table area is very comfortable during mid-day at 95F ambient. A simple fan to increase air flow may be enough.
 
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Several have reported that dash air is capable of cooling rear areas.
 

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I'm considering sacrificing some of the overhead storage space for an air circulation system.
I'm nowhere near that point in the build yet, but I'm confident that with an adequately insulated van (especially the roof), that circulating the air throughout the van while driving will keep it very comfortable.
And probably even while parked in the shade with the van running.
 

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When vans need additional A/C in rear, the normal design is to add a second evaporator in rear, which adds significant capacity. That’s the way my passenger van is and works great.

A duct will do little or nothing to add additional cooling capacity, and will mostly take cooling from front and divert it to rear. I agree a couple of small fans could do the same thing more effectively because they can move more air volume. Also, the more insulation there is, and fewer windows, the more uniform temperature in van will be.

My 2 cents based on industrial refrigeration experience.
 

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I removed the tire changing kit from under the passenger seat and lean a 110vac box fan up against the back of the lower seat area. This helps push cool/hot air from the floor vent to the rear of the van. It's made a huge difference in keeping the van cool/warm by simply circulating air.

My long term solution is to buy an inexpensive 6-8" diameter 12 volt fan (similar to a computer fan) from Amazon to permanently install it under the passenger seat to push air to the rear.
 
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