Back for an update.
We survived our trip to Idaho without AC. Luckily temps were below normal for both the drive up there and back. During the morning drives we could keep the windows closed, use the vents and listen to the radio. In the afternoons as temps rose, the van was noticeably cooler with the windows open, but of course that made listening to the radio futile.
When I got home I brought the van to Alouis Radiator, the shop recommended by Ray, and it was fixed in two days. One day to identify problem and order part (new evaporator) and another to install it. My van is cool again.
Will probably use them for future repairs and maintenance rather than the Ford dealer.
Pic of the evaporator: