After getting the AC breaker box and converter installed and working, I set about getting our fridge in place and powered. The 4-4 1/2 cubic foot fridge that we salvaged from our friends’ trailer was what we wanted in terms of a small three-way unit, but unfortunately, it didn’t work. First, the controller card wasn’t responding, and even though the ammonia system was sealed and I could force the AC heating element to fire up and run, the fridge just wouldn’t cool.
Now, if you’re only used to our modern, AC, compressor refrigeration systems, the ammonia-based systems of a heat-powered system may seem odd. But they are super-quiet (aside from the occasional gurgle) and great for boondocking.
Here’s a nice introductory video on non-mechanical refrigeration systems:
If watching the video is too long for you, essentially the three-way (two electric heating elements or the LP gas heater) system works non-mechanically (no compressor to force-chill the liquid/gas coolant) to cool the interior of the freezer and fridge through heating ammonia to a gas, then taking advantage of the fact that it will condense back to a liquid and the chilled liquid ammonia will become the cooling factor for the freezer and the fridge. Ammonia boils (and thus condenses back to liquid) at -28°F, which is more than enough to keep things freezing in the freezer.
Now, in getting a second-hand non-mechanical fridge system, there are some trouble-shooting things you need to do, unless the owner you’re getting it from can demonstrate that it definitively works. One is to tip it on it’s back for several hours, then raise it up slowly. This is done as an attempt to insure that all the liquids are back down in the reservoir so that the ammonia can be boiled off, and thus cool the interior of the fridge/freezer. The other is to bypass the thermostat’s circuit board and put a heat source (like the electric heater that is installed on the unit or an LP source, like a low flame propane torch) to see if the ammonia will boil out and chill the system.
The most important part of the system is the cooling system, and many old fridges can be rehabbed by purchasing a new cooling system (most for around couple hundred dollars). After I tested the salvaged unit for a couple of days and found no temperature change in the interior at all, I considered this, and started in to do my research, finding out that the shipping charges for these rebuilt/recharged systems can be costly.
It turned out that for us that a (relatively) local seller on Craigslist was selling a 6 cu ft Norcold Refrigerator (model 876 EG2) for about what it would cost for us to get the rehabbed cooling unit for the smaller salvaged unit. And, the seller had it running and cooling when I came to pick it up, so I knew that it was good. (He was also the one that threw the converter in for a song.) This was a good deal, as a comparable new unit like one of these is much more expensive:
The 876 model is a two-door unit, which was a change from the salvaged one, which had a small metal enclosure for the freezer that helped to cool the rest of the fridge.
The two door unit makes for a much more energy efficient and manageable freezer and fridge in terms of temperature. You don’t get ice in the fridge area and the freezer stays really cold.
However, the 876 is taller and slightly deeper than the salvaged unit, which threw a bit of a wrench into my plans. As you might remember from my floorplan, 
there was a covered window behind the fridge, as the fridge needed air space for the cooling vents, and for the heat and exhaust to be vented outside in order to function. One of the major reasons why absorption refrigerators don’t work has to do with insufficient ventilation and blockages in the heating system.
With the smaller, salvaged fridge, I had expected to cut vents into the skinned window and not have to cut the roof, even with the fridge sitting up over the wheelwell (I had expected to use the seat-rail as a support). However, with the much larger 876, I would have to cut off the seat-rail, and rebuild the wheelwell cover in order to lower the fridge as much as possible, and then cut a vent hole in the roof. I had also planned to cut vent holes in the floor to gain air flow and O2 for the LP burner, but with the depth and base construction of the 876, I wasn’t able to do that, so I would have to also cut into more of the skin of the bus in order to get good air flow (and I was nervous about both of these cuts, since I hadn’t done anything to the exterior up to this point!).
Now, I knew that the fridge cooled nicely on 12 VDC, and wanted to verify that it would run well on AC, and was upset when I plugged it in and got no response! But that was because the thermostat circuitry is all 12 VDC, and must have power to run so the AC can kick on the heating element. Once that was rectified, I confirmed that the fridge would automatically switch from a DC source to an AC source (and back) when the AC was available for the heating element. This is kind of a big deal as the electric heating elements are not as efficient as the LP burner, and when available, shore power is your friend for cooling. The DC power is important for while you’re driving (and perhaps for regular running when all the solar panels get installed), and the LP is good for extended boondocking.
But before I could check and see if the LP worked, I had to replace the gas line from the solenoid and, as it turned out in dis-assembly and cleaning, a new burner. The new burner was easily available
(though it used to cost less than it does now!) and needed a new compression fitting at the end of the tubing.
Luckily, I had bought a really nice set of tools for flaring compression fittings to redo the brake lines in my wife’s Daewoo, and it turned out that the gas line was a 5/16″ line that I had a bunch of, so I cut and formed up a new line that sealed up nice and tight, and all worked well.
Unfortunately, as the 876 had been pulled from an RV that had been sitting unused, it was from a unit that had been built in the late 80’s or early 90’s, and had this horrible beige padded covering that stuck out and made the fridge even that much bigger. I had examined the doors and found that the hinges could not only be moved to the right side (from the left where they had been), but also that with the removal of one of the edges the padded facing could be easily removed and replaced with some stained oak plywood, which fit a lot better with our overall look.
I trimmed the existing wheelwell covering and removed the pieces that held it up. Some 2×3’s built up a new floor for the fridge and then I could measure for the area that it would need for the air venting intake and then the hot air exhaust. These presented some problem as the opening I wanted to cut would have gone right through one of the rub-rails. I wanted to preserve these as much as possible so that the bus would keep as much of it’s structural integrity as possible.
To deal with this, I cut the skin between the rub rails to get the opening necessary for the air flow. This was reckoned from the venting salvaged from the old trailer. I ended up cutting down the locking casing for the smaller area so that I could get in and clean out the burner, then cut the vents so that the upper area could be screwed in place and sealed. This makes it removable if necessary, but not with the ease of access of the lower area, yet also keeps the rub-rails intact.
For the top, I, with no small amount of trepidation, cut into the roof. Three cuts allowed the roof to spring up above the reinforcing plates inside, and two triangular metal pieces for the sides created a nice opening for the heat to exit the bus and create a nice draft to pull cool air over the cooling fins of the fridge. It has window screen over it to keep insects out, and will (eventually) get a nice sheet metal cover to keep the rain out.
Inside, the air was channeled to the outside by some wooden ducting, sealed with weatherstripping and screwed in place. The actual flue from the LP burner would run up against the metal, keeping the burning hazard at a minimum, and allowing for plenty of air movement.
Wires were run for the DC and AC power sources and the fridge now runs like a top, even bringing some pop-ice sticks to a frozen state within a few hours.