The heater and fan along with the front windshield defroster do not work.
How to fix a heater that no longer works on 1994 Volkswagen Jetta
If the fan (Blower Motor) is not working, you will not have air flow to any mode selection (floor,vent,defrost). Power source problem could result in the blower not working, as could a resistor or blower motor failure.
the fan switch itself has a high failure rate on that car. If you do not have the ability to perform the needed testing to pinpoint the problem you may want to try a switch- they are cheap and easy to replace. Greg