I've got a Ford e350 (1996, 5.8L). Our front vent A/C works well, but the back blows what seems to just be vent. Not heat, but about the same temp as outside.
We just recharged the A/C (by mass, after pulling a vacuum). We had to replace both evaporators since they were leaking (there's one in the front, and one in the back, working together).