I have been trying to improve both the performance and safety of my Norcold 621. Pretty common fridge.
I was experiencing long initial cool down times and slow recovery when opening the door a lot. Some areas were colder than others in the main compartment. There was a substantial amount of ice build up on trips of a month or longer. Defrosting a fridge didn't seem like a task to do on vacation. Seeing the fire problem with these types of units also concerned me. I like to roast marshmallows outside not siting at the dinette.
I explored several products to fix these shortcomings. To address the fire safety issue I installed an ARP fridge control unit with the optional fan control. This product will limit the temp of the unit with a sensor that is mounted on the flue. Seemed to make sense and it works well. To address the uneven cooling inside I added a Fridge Fix interior fan that blows air across the cooling fins at the back of the cooling section. This unit has made the temp even and has eliminated the frost problem. When I turn the unit off I have no more water to wipe up than a single napkin will hold. It also speeds up the initial and subsequent cooling periods by blowing the air on the fins and transferring the cold more quickly. I am planning a trip over Memorial Day and from the time I turned the unit on until it reached normal operating temp was just under 5 hours which is the new normal. It does no good to turn your control to a max setting because the cooling unit is temp controlled so it can't be forced to cool faster than normal. All you can do is to increase the efficiency. To address the efficiency I added 2 Corsair 120mm fans to my upper roof vent. These fans are controlled by a sensor from the ARP. They both suck air from below and exhaust it out the upper roof vent. The purpose of these fans is to remove the heat buildup from the cooling process and make the fridge more efficient by improving the heat transfer, which is the main objective. Both the interior fan and the exterior fans are wired into the ARP fan control circuit and they only operate when the fridge is producing coolant, the only time they need to run.
The installation of these three items is not complicated and it has improved my performance more than I anticipated.
I thought it was time to give this final update because most of us are heading out on adventures in the hot summer temps that we all wait for. I don't know about about you but my grand daughter likes hard ice cream and I now don't have to disappoint.
If you are having issues then try these solutions, you will be satisfied. Have a great summer!