My 1999 Toyota Camry lost all by the high and medium-high fan speeds a few years back, then one day I had only the “high” fan speed. A little bit annoying, but something you get used to. I ignored it because I figured it would be expensive and time consuming to get fixed… however the solution turned out to be very easy. (click on the photos to enlarge)
The simple part below (from Amazon) is all that is needed to fix the problem. It took me about 20 minutes to replace, mostly just because the part is a little hard to get to.
If you look under the glove box area, there is a black cover that you carefully remove, this will expose all the wires and controls underneath. Then on the side toward the steering wheel in the far upper corner you will see the JA1334 resistor. Remove the 2 screws holding it in and it will slide right out. Unplug the connector, and plug the new part in and screw it back in (easier said than done). But once it is in, you should now have ALL your fan speeds back!
Here is a look at the old one I removed, you can see how worn and corroded it had become!
**disclaimer: I am no auto technician, replace at your own risk**