This is usually caused by teh "blower motor resistor", an easy to change part. It can be the climate control module, but usually is the 'resistor'.

Search for "2003 SLK320 blower motor resistor" or "Chrysler Crossfire blower motor resistor" and do not pay over $30 plus shipping for it. It is VERY easy to change, there are threads here on the procedure and there are youtube videos as well.

Fuse 34 or 36 (depends on year and trim level) will remove battery power from the blower.