That's the 105/115 switch. At 105C one wire gets a ground signal to turn on the aux fans. At 115C another wire gets a ground signal to cut the compressor. Maybe water pooled on the switch and grounded the wire the cut compressor wire. Or the plastic housing has gotten brittle with age and water seeped in.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD