Heater / AC Dash Switch

My wife's 2002 Sundire, 4cyl, 118K miles. Everything works perfect, except the fan switch on the dash only works on "Off" and "High". Not the intermediate settings. Obviously, more a nuisance than a real problem, but would like to fix it cheaply if possible. Fan works, A/C is cold, Heater works, Defrost works, etc. Only problem is the switch. What should I check? Any advice appreciated. Thanks.

JB