June 27, 2018: The reefer (absorption refrigerator) in our trailer is a Dometic DM2652 and many times when the outside temperatures are 80+ degrees it has struggled to keep the inside refrigerator temperature at 40 degrees or less, even with the thermistor control slid up as high (Cold) as it will go). In order to solve this problem I have made a couple of modifications.
I use electronic sensors inside the reefer and freezer with an outside monitor to keep tabs on the status of cooling. The monitor also records minimum and maximum temperatures.
The first thing I did was install two 12 volt DC fans to the outside lower section of the reefer. I bought the Valterra one with the thermistor switch and another computer-type one. I wired these in with three switches. The first is the master on/off switch and it is mounted inside the trailer. This switch also has a small red lamp inside to indicate the switch is on. The other two are micro switches mounted on the back of the reefer. Using these switches I can run one or both fans either controlled by the thermistor or with the thermistor bypassed. Actually, I need to test the thermistor because I have never observed the fan/s running with the thermistor controlling them. The purpose of these two fans is to force air up over the coils in back and out the top vent.
After using them for several days of camping I cannot say for sure they really have helped a whole lot, so the next thing I did was buy one of those small battery powered fans that go inside the reefer. I initially put this on the bottom shelf, but again this did not seem to really help much with the overall temperature inside, although it may have made it more equal throughout the interior.
The next thing I tried recently on a June trip down to Key Largo (with some pretty warm temperatures during the day) was to reorient the little battery powered fan to the very top shelf and aimed at the fins near the inside thermistor. Even though the air output of this little fan is very low this, in conjunction with running both the fans in back really seemed to help keep temps lower. I observed low temperatures as low as 33 degrees, but primarily the temperature tended to hover in the 37-39 degrees (F) range.
So, I figured that if this little bit of air blowing on the fins made a positive difference, a lot more air would make an even better improvement. I bought a small two fan assembly with LED light unit off eBay for $35 including shipping and installed it a few days ago right on the fins.
The unit has two switches; one for the LED and another for the fans. The instructions mention several different ways of wiring it up, but I sort of did my own thing with the installation. I only want to fans to work if the reefer is turned on, so I pulled the interior light switch and after confirming the wiring with a multimeter I soldered the power wires to the correct wires going to the interior light. Worked great.
Here are a couple of pictures.
Since we have an interior light (LED) already I doubt we will ever use the LED on the fan assembly. I used Gaffer tape to dress the wires inside the reefer and left the entire length of the wires intact since there is a built in fuse near the free end. I want to see how the Gaffer tape holds up inside the cold reefer.
At this point I have not tested to see if this new fan setup will do what I hope and have read that it should do, which is to lower the temperature inside substantially to the point I can move the controlling thermistor down a bit and keep the inside temperature at 35-37 degrees (F). But, in another week or so we will be leaving for a few weeks out West to Colorado. It will get a thorough test and I will edit this to report the results.
Update 9/10/2018: After using this setup for a few days camping, while the cooling was better, it was still not as good as I wanted it to be, so I moved the interior double fan over as far to the right as I could so it would blow a bit more air onto the thermistor. This really helped.
On our last trip a couple of weeks ago from Florida to update New York and back the refrigerator temperature was normally staying around 35-39 degrees and we were encountering outside air temperatures of 90+ degrees F. A few times overnight it got down to 33 degrees and only rarely got above 40 degrees briefly if the fridge door was left open for awhile while someone looked for something inside.
I think this has solved our reefer cooling issues.