Our goal has been to keep the freezer side of the split box at about 0 degrees and the refrigerator side at about 40 degrees. The evaporator plate is mounted in the freezer compartment. The refrigerator side is cooled entirely by spillover from the freezer side. We concluded after operating a couple of seasons that the box insulation was not sufficient requiring the compressor to run too much. Many other Island Packet owners have experienced the same in many different models. It is my understanding that the manufacturing process on newer models has been changed to minimize the incidence of voids in the insulation. We found a site, www.rparts.com that sells components for refrigeration systems, including box construction materials. Since the box was over-sized we decided we could add insulation to the interior without great sacrifice of space. We also did not want to remove or alter the countertop in any way. This meant working inside the box which would prove to be very challenging. We ordered vacuum panels which were custom made to our specifications. These are 1 inch thick cut to our dimensions. The box is an irregular shape, so all panels had some angles. They also had to be size to fit through the access opening. The vacuum panels have to be handled carefully and well protected as any puncture will reduce the effectiveness greatly. The panels have an R-value = 28. To protect the panels and provide a new interior surface we orders sheets of protruded fiberglass. We then cut pieces to form a new interior. Construction then involved gluing the vacuum panels in place using insulation foam, and then gluing the fiberglass sheet over the panels and finally using an epoxy putty to seal all joints. The insulated divider between the freezer and refrigerator compartments was removed, cut down on each side to the new dimensions and then refitted. While it was out we added a electric spillover fan which is controlled by its own thermostat.
One last upgrade was to add an electronic module to control the compressor. The objective is to run the compressor at the slowest possible speed. It is more efficient to run it slower for longer periods of time. Depending on the demands, this module adjust the compressor speed to achieve this objective as much as possible. It also has manual override which is used to cool faster such as when restocking.