The resistor pack (or controller, for the automatic HVAC systems) that installs in the duct near the blower motor is for the lower fan speeds. If yours is running on High at all times, it sounds like the high-speed override relay is stuck on instead. This is the relay that closes when you dial up Max A/C.
If the firewall layout of yours is similar to my '93, you've got a MaxiFuse Relay Center under a cover on the firewall, with a row of relays on it, one of them being the high-speed blower relay. I don't have the specifics here with me, but maybe that'* a direction you can look into.
-- Andy Green