Just wanted to post this for reference in case someone else encounters
the same problem. My heater/AC blower stopped working except on the High
setting. Classic symptom of a blown resistor pack. Turns out the contacts
had rusted apart on mine.

The resistor pack is attached to the air box on the passenger's side of
the dash. It is easy to locate and replace.

There is a plastic cover that comes off by removing a Phillips screw from
the front and loosening a bolt underneath. Follow the wires to the
resistor unit. Unplug the wires. The unit is held in by two sheet metal
screws (7mm). You may need to loosen the nuts that hold a vacuum actuator
in place in order to get to one of the screws.

Remove the screws, pop the unit out and replace the unit.

Plug in the the wires, replace the sheet metal screws, tighten the nuts
on the vaccum actuator, and replace the cover.

I couldn't order the resistor pack through my local NAPA store. They said
it was a dealer-only item. I ordered one online. It cost me about $5.50.