Don't know this particular model, but the percentage bet on these issues in general application is as follows:

a. Nothing but high blow = resistor pack. The "normal" speed of the fan is high, and all the other speeds are as a result of the power going through resistor(s). It is likely mounted so they hang into a duct/plenum somewhere.

b. If the air doors move via vacuum motors, nothing but defrost is the default setting when the vacuum source goes away. Look for a broken/disconnected manifold vacuum line that supplies the system.