Good info, Richard. As far as the heating stage, if you only use the unit when the sun is out, then it shouldn't be too hard to add a solar heater section.
If you have time on your hands and are a capable scrounger, then the purchased parts can be kept very affordable. I think most structures have a lot of low-hanging fruit when it comes to boosting efficiency and reducing interior heat (before the cooler is even turned on).
I experienced significant savings from installing an attic fan, which only used the watts of a light bulb, and cooled the attic...
I also hung shade cloth from the edge of an eave, to shade the sunniest outer wall, and especially the glass in the windows. Before that, I could feel significant heat coming from the glass.
Later, certain windows were covered by a large single pane of glass as a second layer (double panes are common now), but also...it wasn't just the second pane that reduced heat passing from the outer pane to the inside of the old house.
The stock windows have to be loose enough to open and shut, so...there is always leakage. The large single pane was well sealed over all of the stock window.