What's wrong with my A/C/Heater?

If you're talking about MAX that is for high fan, then it means your blower motor is going out.

You have to turn the dial to max in order to have what come on? The blower or the heat?

You are correct, the freon level isn't going to affect the heat unless you have an automatic climate control temperature system. The blower speeds are controlled by either an electronic controller or a resister assembly - depending on the year, make and model.

There are alot of common problems with newer cars doing this, and most times it is not the blower motor. Like for instance, Newer GM's are notorious for the switch (The one you turn for the fan to come on), those go bad quite often, you can probably find one in a junk yard for $25.00 or so. Also, the newer chryslers there is a component (I believe they call it a resistor) under the dash on the passenger side. That is extremely common on those. If you go to a chrysler dealer they will know what your talking about. those are about $50.00 or so....

Sound like the blower motor is going bad or maybe the control valve is stuck close or don't open all the way

fan motor is going bad or

a critter built a nest in the blower wheel. preventing flow

the heater and AC are two different units. sound like what your saying it is the switch on the dash.