Fan control for air conditioning and heater control of a mercedes benz A 160 is only working in the top fan speed position. i cannot find a way in gaining access to the center console and switch assembly. how does it come apart and how does it work?

A faulty blower motor resistor is more than likely the culprit. Follow blower wires back from blower motor to nearest connection which is normally the resistor pack. Replace resistor.

This may be an easy one. Since the top speed works, it is not the motor. But the way lower speeds are achieved, is by the insertion of resistors in series with the motor. These resistors get hot, so are inserted in a resistor pack that is located in the main air path in order to achieve cooling. But they still burn out from overheating. Follow the wiring to the motor, and you should find the resistor pack. If you check it with an ohmmeter, you will find an open circuit on the lower speed connections.
If not, then is it not the resistor pack, and the next suspect would be the switch or climate controller.