Defroster not working?

Yeah, it sounds like the mode door actuator is the issue. Here is the material from the manual. It is not terribly detailed but basically the mode actuator should be on top of the HVAC housing behind the glove box.

Here is a guide that goes through the basics of the blend door which is a different door but gives a little more general information:

https://www.2carpros.com/articles/replace-blend-door-motor

Run through this material and let us know what questions you have. Thanks