AC Unit Ventilation System

The room window 5000 btu AC unit is installed inside the sealed compartment in the rear cabinet. It requires ventilation - fresh air goes in through the sides and hot air exits out through the rear. To make this possible I had to build the conduit connecting the AC compartment with the outside of the van through the rear door. The conduit has three channels: left and right  for air in, and central for air out. It also has two parts: the van part attached to the cabinet, and the door part inside the door. Since the door opens, these two parts should be connected via the rubber seal. The whole construction has to be moisture resistant, since some amount of water can get from AC exhaust and from outside.

It happened that designing and fabricating this system was significantly more complicated than I originally thought and took at least triple  the time that I planned for it. The main difficulty was that all pieces of this conduit have different splicing angles at the connections, which was not possible to imagine or calculate. So I used the cardboard models. However, the cardboard pieces being thin, did not model well the 3/4" thick plastic trim panel that I used for this construction. This resulted in inevitable mistakes and a lot of tweaking the roughly cut pieces until achieving reasonably good fit.

The images below show the fabrication process and details of design.

First, I made as large as possible cutout window in the door. The internal door panel already has a cutout, however it is small. So I made it larger by cutting out the top. Then, I  accordingly cut out the outside panel and filled inside of the door with rigid foam insulation pieces glued to the sheet metal of the door. Thus I created a firm insulated window box in the top of the door. The bottom wall of the window is sloped outside to let the occasional water escape out.
 

To make the conduit, I cut the pieces of the plastic trim board from Home Depot, and screwed them with pocket screws to the rear wall of the cabinet. The vertical walls are tweaked to match the profile of the door and the horizontal part has significant slope to connect the bottom of the AC box (higher) with the bottom of the door cutout (lower).

The next step was to make the dividers to separate the conduit into three separate channels. 

I started from shopping for the outside grille. I could not find one piece of a needed size, so bought two white ventilation grilles from Lowe's and joined them together to have one 10x30  piece. I marked on the door the position of two side dividers of the grille, and installed two dividers in the door cutout to match those of the grille.

  

Then I started making the conduit dividers, which happened to be the most painful part.  These two pieces connect the sides of the AC frame with the dividers in the door and have to be fitted relatively air tight. The pieces have the irregular form and every edge has individual slope that has to be matched with the edge of the existing surface they attach to, especially at the top, which has quite complicated form and is hidden from outside view. A lot of trial-error tweaking and yet couple mistakes have been made to be corrected later with small pieces cut to the place and glued in.

 

The last step was to attach the seal, for which I used the Frost King EPDM ribbed profile Weatherseal from Home Depot




 


The final look of the door with the grille is below. The bottom edge of the grille has a spacing between the grille and the door grace to rib there, thus letting water to escape. The appearance of the grille is not perfect because I had to manually reverse the direction of each louver from inside to outside and was not able to achieve uniform spacing.