Well, I know it's obvious, but make sure the EC button sin't engaged for starters.
Next, turn the wheel to "low" and see if the compressor engages. If not, try the top button on your right hand side of the ACC panel, used for defogging. It engages the compressor for dehumifying. If the compressor engages, then your ACC panel is going south.
If not, could be a compressor problem. Or, you may have a leak, and the system is out of coolant. Since the coolant provides the lubrication for the compressor, it won't turn on when it's low.
You'll probably need to spend a few bucks on diagnosis. Your main components are:
Evaporator. Source of many leaks, and $$ to replace.
Expansion Valve. They wear out.
Receiver/Dryer. Another item (filter) that wears out.
Condensor. These can break too, but not all that common.
ACC Panel. Common failure on W201 and W124 cars.
You'll need to have the high and low side pressures checked and/or the system checked for coolant and leaks.
1998 C230 "Black Betty"