Dometic does include a ventilation fan for fridge installed in a slide out in outside compartment due to the upper vent being on the side wall of slide out vs having a roof vent. Helps with draft flow of cooling air.
OEM fan would be center line of fridge just above absorber tubes. DC power would come from 12V DC terminal block by control module and would have in-line fuse (3A). Fan would be controlled by thermostat installed on far right fin of condenser (top of fridge)
IF fan is running continuously....either t-stat is stuck closed/failed
OR
previous owner installed fan and didn't use a t-stat for control...maybe an on/off switch.