This just recently happened.
The interior fan only works on high speed.What can cause this and how do I fix? on 2001 Toyota Highlander
Usually the blower resistor has failed when that happens .Blower resister should be in the blower motor housing under the glove box area of the dash. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online