My 2006 blows on 1, 2/3, and 4. The reason for "2/3" is because 2 is the normal medium/low speed, while 3 does not change up faster to go to medium high. It still works, but just on 2's speed.

Know some people say that their fan speed issue happens where the fan doesn't work at all, but didn't know if something like this is related to the motor resistor, like here

 

The blower gets 12volts from a fuse, well thru a relay from a fuse when system is on.
It is safer to run Ground control wires around a vehicle than 12volt wires that could short, so pretty much all control wires for a vehicle are ground wires

The fan speed switch on the dash is the Ground for the blower motor, when on High blower gets a direct ground from the switch, doesn't go thru blower resistor.
Blower resistor is just that, it has 3 different resistors, for the 3 different speeds.
If a resistor was bad I would expect no blower except high, since they are hooked up in series, chassis ground-----resistor----resistor----resistor-----blower
So problem could be in the switch.

But I would pull out the blower resistor and test it with OHM meter since it isn't that hard to get to, if it all checks out then you will need to dig into the dash.

Just as a heads up the blower resistor connector did have issues, if there is corrosion you could have speed 3 and 2 is the same, not the other way around, basically a ground short to lowest resistance.

Speed 1 goes thru all 3 resistors
Speed 2 goes thru 2 resistors, so less resistance and higher voltage to motor
Speed 3 goes thru only 1 resistor