One other thing- when I picked up the van the rear A/C fan was blowing, but only warm air would come out of the side vents. No air was coming out of the roof vents. I did some searching online and found out it was most likely one of two issues, both related to the blend door, which diverts air either past the rear heater core to the lower vents along the drivers side panel, or to the roof vents for A/C.
The blend door is actuated by a vacuum line, so one possibility is that there was an issue with that, but when I tested it at the actuator I was getting plenty of vacuum. So I pulled out the blower motor from the rear A/C unit (4 screws) to access the blend door, and the linkage between the vacuum actuator and the blend door was broken. I ended up securing the blend door in the "A/C" position since I don't anticipate needing rear heat for several months, and I haven't looked into whether or not I can get a new blend door for a reasonable price.
After pulling it apart and looking at it, the linkage ssems to be very weak and prone to breaking, so if anyone else is having this problem it is a reletively easy fix.