If you post the model number of your fridge, it may help. If you open the outside access panel, you'll see a wiring diagram and the model number. You may (should) see the fan on the wiring diagram.
You should also make sure your thermistor is pushed up as high as possible. The thermistor is clipped to a fin inside the fridge with a white plastic clip. You slide the clip up and down to regulate the temperature. Sometimes the thermistor slides down inside the clip, but you can't tell. So make sure both the clip and the thermistor are up as high as you can get them.
Reading other posts, it seems like the external Dometic fans are not particularly great. A lot of folks have replaced them with computer fans that run better and blow more air.
I'm sure others will chime in.
BTW - post your model 5th wheel and year also. Someone with the same 5ver may already have figured out the solution to your problem.
1988 Coleman Sequoia - popup (1987-2009)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10