From time to time I've periods where my 3.7 CF frig (the DC 0051) would not cool below about 50 degrees, even if running constantly. I'd pull it out and it would do fine on the bench.
As I said in a previous post http://www.sportsmobileforum.com/vie...p=45922#p45922
, the Norcold manual for the frig says the small external fan should come on when the air around the frig exceeds 90 degrees. I checked mine by putting the frige in my sauna and slowly raising the temperature. The fan did not come on until it was about 125 degrees.
The heat that is removed from inside the frig needs to get dumped via the coils into the space behind the frig. When the temperature difference between the coils and the surrounding air is not much, the heat transfer is almost non existent so the frig runs continuously but it can't get rid of the heat.
To minimize that problem you need to maximize air circulation across the coils. SMB usually provides a very tight enclosure, with virtually no space on the sides. The bottom of the frig is about 1/2 inch off the shelf, and there is maybe 1 inch across the top. Air circulates by convection, and should be "helped" by the fan if it gets too warm.
The frig fan is located just below the compressor as seen below.
If the van is very warm inside the efficiency (ability to do heat transfer) is very poor. I put a thermometer with a probe behind the frig and saw that the temperature climed a good 20 degrees or more in that space when the frig kicks on.
I modified my system to increase the air flow by two methods: First I hard wired the frig fan to a switch to my 12 volt system so I could turn it on well below the auto activation temperature [Again, the manual says it is programed to turn on at 90, but my test indicated is came on at 125 degrees.]
I also cut a special opening into the support shelf behind the frig (directly below the compressor and the coils) and added a second small, very quiet fan to further increase the air flow. In my case I have a drawer below the frig, with open space at the back of the drawer which goes down to another space with my espar and a open return air. The new fan pulls air in from the floor up behind the frig and across the coils, and out.
I drilled a set of holes based on the layout of a 4" case fan, as seen in the next photograph.
The zip ties were used to "hang" the fan, and were later pulled tight to slightly compress the gasket.
The next three photos show the fan installation, which I did using a foam rubber gasket and zip ties, to help isolate vibrations.
Here are the fan specs, under the "Silent 12" column. Notice the decibels are only 20, and the current for the new fan is 0.08 amp (not an issue when the sun hits the solar panels).
Both fans are controlled by a DPDT switch which is ether OFF, one
fan on, or both
fans on. I kept the temperature sensor in place so I can monitor the back side space and the effect of the fans.
Its no fun taking a trip into the boondocks, wondering if your frig will do its job. I have had no problems since this modification, even in very hot whether.