My Isotherm never would cool the "fridge" section very good since the day I bought the camper.
Tried all the usual - Pre-cool the fridge a few days before the trip. Put some water bottles in the fridge while pre-cooling. Load the fridge with cooled items. Tried the fan. Middle shelf is the best.
At my wits end, I came up with my own fix. Saw it here on WTW or a boating forum. . .
The freezer section is the only thing cooled in an Isotherm. (Similar to your home reefer) The capillary tube for the thermostat is on top the freezer box. I moved the capillary tube to the larger "refrigerator" box area.
The capillary tube is what senses temperature and controls the thermostat.
The refrigerant lines & capillary tube sit on top the metal box freezer area.
Take the door off. Gives you room to work. Remove the two screws you see in the above picture. You can tip the box down and see the refrigerant lines (be careful, don't break or damage them) and the capillary tube used to sense temperature.
Move the capillary tube from the top of the metal freezer box and route it down the outside of the metal box into the refer section.
Place it in the back of the "fridge" section. I used stick on cable tie holders. Don't break or kink the capillary tube.
My refrigerator section will now stay at 38 degrees, on 5, on the hottest day. I still use the portable fan. Place it on the middle shelf.