There should be two switches on the dryer - one with spade lugs on it, the other with pigtail connectors. The one with pigtail connectors is the fan trigger. Bridge the harness side contacts and the fan should engage. If so, the switch is bad. If not, the fan side is bad. The switch goes into the refrigerant system so replacing the switch means evacuating and refilling the system.

Later cars have additional circuitry to trigger the fan and cut the compressor based on coolant temperature.

Sixto
83 300SD can be yours
98 E320 wagon