Thank you Bill,
My Frigoboat has a Danfoss control 102N4030 which runs the compressor and the fan
There is a switch with a red light, which seems to control the fan. When I turned down such a switch down the compressor started, and the freezer is now getting cold but the fan is not running.
Do you know what for is the switch? Could it be that something is wrong with the control?
I agree that the refrigerator is old, but my experience is those older refrigerators can last forever. My grandmother refrigerator is still running after more than 60 years of use ;).