We purchased the Coleman Mach 8 Cub 9200 BTU AC unit to replace the original Armstrong unit. This is the newest version of the Coleman "Polar Cub." It has a low profile (8-1/4" tall), low power demands (should run on a Honda EU2000 generator), has an optional heating coil, and once our insulation is in, should be plenty of cooling for our purposes.
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The process of purchasing exactly what we needed was a little difficult, so I am posting lots of detail here in case it can help someone else. I purchased 47201A876 rooftop unit, 9430D715 ceiling assembly, and 47233-4551 heat kit from CampingWorld.com for a total of $905.64. There were lower listed prices elsewhere, but once you include shipping, Camping World was the cheapest I found at the time. You can sometimes find the rooftop unit, ceiling assembly, and heat kit for cheaper on Amazon.
Update for 2018: Coleman has released a new version 47201B876 Mach 8 Plus Cub rooftop unit. The Mach 8 Plus has a redesigned outdoor fan to reduce outside fan noise and improve heat transfer across the condenser coil. Find the new Mach 8 Plus Cub rooftop unit on Amazon here. The same ceiling assembly, heat kit, and condensate pump will fit.
After placing my order, I had some additional correspondence with the manufacturer of the Coleman Mach 8, Airxcel Inc., and learned that a condensate drain system is not included on the Mach 8 Cub, even though it is standard on some of the larger units. As designed from the factory, the condensate would run down the outside of the Airstream. That won't do, so off I went to MarkariosRV.com (the only website other than eBay I found that had the 47203-3091 condensate pump kit) and $89.38 later, I should have everything I need.
Now, to assemble the bits. Here's our new AC.
Remove 4 screws, shroud off...
Here's where the condensate pump is going. Note the two small holes drilled in the bottom of the pan. That's where the condensate would exit the pan to create an ugly streak down the side of our nice shiny house. There are a bunch of holes drilled in the plastic pan, but these are the only two I should need to plug.
Test fitting the condensate pump. Looks good.
The fan blade needs to come off so we can access the wirebox below it. One screw, star bit.
Now the cover for the box. One hex nut.
Nice view of the capacitor and terminal blocks. Airxcel was kind enough to manufacture all these parts with spade terminals, so we don't need to splice any wires together.
Now, we need to remove the evaporator cover. Four hex nuts.
OK, evaporator cover off.
This aluminum tape comes off to reveal a notch in the plastic ...
... which is a perfect fit for the drain insert included in the pump kit.
Probably would have been easier if I put the tubing on first. The condensate pump is using 1/4" ID (inside diameter) tubing, and the kit includes an adapter for the 1/2" ID tubing I'll be using to run the drain through the wall of the airstream, behind the refrigerator, and onto the ground.
Now, before I close up the evaporator cover, I want to mount the heating coil. You can do this from underneath after the unit is installed, but it'll be easier now. Here's the heating coil kit.
Attach the mounting bracket. 2 wing nuts.
There are two threaded studs already in the return air opening for mounting this heating coil.
Two wingnuts, and it's mounted. There's a relay inside the electrical box on this coil that rattles a little. I'm hoping it won't be audible when the AC is on. There are now two electrical wires hanging through the return air section, which will both plug into the ceiling assembly.
Now, back to the condensate pump installation. Evaporator cover goes back on, 4 nuts.
Need to remove this strain relief bolt. One nut.
There is an indentation where we need to drill a 7/32" hole for the other mounting bolt.
Now I need to plug those drain holes. TremPro, because this is for an Airstream, after all.
Not pretty, but it'll hold water.
Pump goes in. The directions say to install the bolt downward through the hole I just drilled, but that doesn't make sense to me. I installed upward like the opposite bolt. There are two nearly identical nuts supplied in the kit. Ask me how long I spent trying to thread the 8-32 nut on the 10-24 bolt. Big nut goes on the ground wire and newly installed bolt, little nut anchors the ground wire to the blower motor.
Tubing attaches to pump standpipe.
Wires into the wirebox through the plastic entry clamp.
Black spade to purple block, white spade to yellow block.
Wirebox cover goes back on, one nut. One zip tie to keep the pump wires away from the sharp edge of the condenser coil bracket.
Fan blade back on. One screw. Check out the crazy angle that compressor is mounted at. That's not for lack of space -- someone at Airxcel clearly doesn't want the compressor vibrating in the same plane as the blower motor. Clever way to make it quieter, I'm guessing.
Cover back on. 4 screws.
Checking the drain holes for a good seal. You can see the foam around the square roof opening that compresses to form a water-tight seal. This will install with just four bolts, one at each of the corners of the roof opening. The old Armstrong AC installed with about a fifty screws and a gallon of Vulkem. I spent most of the rest of today removing said goo from the roof. I'll be bucking rivets into the screw holes next weekend.
Once I'm done prepping the roof, probably weekend after next, I'll install this unit. Then, we'll have to wait until the interior skins are in before we install the ceiling assembly. ETA on that -- March-ish.
See Part Two here.