More Air Conditioning for the S-280 Military Shelter

Purpose: to show a way to safely mount a 13000BTU air conditioning condensing unit to an S-280 shelter, and then construct the evaporator and blower assembly inside. Yes, I am building my own air conditioner out of parts. It may not apply to your shelter, and we assume no responsibility for anything.

Click on the little picture to see it larger.

Oblique view shows some of the mechanical details. It can be seen that the bracket unit is mounted to the removable hatch. This hatch is supposed to be removed, and the military air conditioner slid into the hole, and then attached to the hinges which can be seen on the top of the box. Unfortunately, the military air conditioners are not to be found. On the right side of the box (see last picture) an 8000 BTU air conditioner was installed. It weighs about 65 LBS and this was deemed suitable for the hatch frame to support. A 13000 BTU unit weighs too much, so building a split system with only the compressor, condenser, and condenser fan mounted on the box was deemed a good solution and avoids cutting large holes in the roof for an RV air conditioner, and the associalted clearance and durability issues. Note the bracket on the top of the condensing unit is temporary.

The problem is that during summer duty, the shelter (box) hatch (rear door) gets opened and shut repeatedly, letting the cold air out. Furthermore, measurements were made indicating that when it is 100 degrees outside with sunshine, the shelter's outer skin is 120 degrees. With the 8000BTU unit running, the interior skin is 100 degrees and the interior air temperature is 78 degrees. This would be acceptable if the hatch were seldom opened, but the usual situation prevents that, and we end up with about 85 degrees. At that temperature, the radio gear begins to get uncomfortable, especially under heavy use. It also adds heat to the shelter. The total heat load to the interior due to electronics is about 800 to 1400 watts.

Details of the construction are shown here. I had never done anything like this before, so I took the first goal to be strength and safety for this heavy unit. A hasty spray with some brown paint took the bling (shiny metal) out of the equation. It wil be properly painted later. First, the upright supports were put in place, then the bottom tray was assembled. Finally, the diagonal supports were put in place. Careful measurements of the condensing unit width allow a snug fit in the tray. Be sure to account for the thickness of the heads of the bolts which hold the tray and bracket together. This was about 1/4". A Milwaukee "sawzall" was used to cut the metal. The hardest part of the job was putting the 65 LB condensing unit on my shoulder and carrying it up the extension ladder to the roof of the truck.

Here is another picture of the underside which may clear up some details. Once the job is completed, the protrding angles will be sawed off flush with the bracket and tray assembly for a neat job.

Here is what it looks like on the truck so far. Once the copper tubing is soldered in place and the electrical wiring run, the condensing unit will be bolted int place with 1/4" lag bolts through its thisck bottom plate, and some #12 sheet metal screws through the sides. Care will be taken to avoid the coils, plumbing, and compressor! Lockwashers are always used in these applications to keep the scres and bolts from getting loose. In any case, proper PMCS requires them to be checked periodically.