This series features what I call “RV Gremlins,” those pesky little troublemakers that seem to pop up out of nowhere and then just as quickly disappear. In Part 1, I looked at the gremlins that live in lead-acid batteries. In Part 2, we looked at the mysteries of 12-volt wiring. Today, we’re trying to figure out the gremlins in RV absorption refrigerators.
Everything works fine when the rig is sitting in the driveway getting ready to take off on a trip, but the minute you plug into the campground source it either doesn’t work or doesn’t work efficiently enough. I get questions every day about how something worked fine for several weeks, then it didn’t, only to start working again. Let’s take a look at some of the major appliances and what situations, or “Gremlins,” they have.
RV absorption refrigerators
The key to getting an absorption refrigerator to cool efficiently is understanding how it works and the factors that can affect its operation and efficiency. Dometic and Norcold are the two most popular absorption refrigerators and work pretty much the same. They utilize a cooling unit in the back that has a container called an absorber vessel with a rich solution of ammonia, hydrogen, water, and sodium chromate.
A heat source from either a flame from LP or a 120-volt heating element heats the solution. This then causes vapors and gases to rise up the pump tube to the condenser fins at the top, the freezer section.
How RV absorption refrigerator systems work
The short version of explaining how it works is that several chemical reactions and flashes happen in the cooling unit and all the rich solutions must zig-zag back down the cooling unit tubes by gravity. If the rig is not level, it could cause the rich solution to pool or stop flowing in an area. If this happens, it will get very hot and start to dry out and flake, eventually stopping the flow and ruining the cooling unit.
This is a common problem as most RVers bring their rigs to their house before taking off for a trip to cool the refrigerator down and pack the unit up. Most driveways are slanted for rain runoff and are beyond the acceptable level recommended by the refrigerator manufacturer. They recommend no more than 3° side to side and 6° front to back. They also provide a bubble level to show what is acceptable. However, most owners don’t think about being level as they are not sleeping in it and don’t notice the angle. As the cooling unit gets more and more plugged, it becomes less efficient until it stops cooling.
RV absorption refrigerator gremlins
Where do the gremlins hide? All refrigerators cool efficiently to below 40 degrees when the ambient temperature is cool, like in the 65-70 degree range, unless the cooling unit is plugged more than 50 percent. If you are having insufficient cooling, check the operation on both LP and 120-volt modes. If it works as designed on one mode and not the other, it indicates the cooling unit is fine, just a gremlin in the mode that is not working.
However, if it’s not working efficiently on both modes, check the thermistor on the evaporator fins as this is the temperature monitor for both modes. If it is placed too low and in the middle of the fins, it will sense a lower temperature and not turn the unit on as often. If it is covered in frost or ice, it will indicate it’s cold enough. Keep in mind these units are not self-defrosting, so you will need to keep an eye on the freezer and evaporator fins especially if the next issue happens!
How to get the system to work the most efficiently
Warm, moist air and poor air circulation can cause hot and cold pockets in your refrigerator. This not only causes excess frost but also inaccurate temperature readings. Check the door seals periodically to make sure they seal properly by placing a dollar bill between the door and the refrigerator frame and shutting it. When you tug on the bill, it should have a slight resistance. If not, it’s letting air from inside the rig into the refrigerator cabinet and it will cause the unit to work harder and not cool efficiently.
This is a common issue as RV owners like to put heavy liquid containers in the door shelves just like at home for easy access, and then bouncing down the highways causes the door hinges to bend or settle. The warm, moist air from inside your rig will cause additional frost and ice buildup and inaccurate temperature readings.
Do not load your RV’s absorption refrigerator with warm food or canned food that is not cooled. Try to bring everything down to below 40 degrees fast. Make sure you have good air circulation in the cabinet—do not line the shelves with plastic or anything that will restrict good circulation. I recommend using a 9-volt fan to help move air inside the cabinet.
Last check: The house batteries
Another issue could be sulfated house batteries. The module board needs 12-volt DC power on both the LP and 120-volt side, as the eyebrow board runs on 12-volt and provides information to the module board. If you are having intermittent issues or insufficient cooling, use the 12-volt power booster to identify it’s not the house batteries.
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook.”
Read more from Dave here.
Pros and cons of residential refrigerators in RVs
See how RVtravel.com readers reacted when we first discussed residential RV refrigerators. At the time it seemed they were being installed in most large fifth wheel trailers. Among the topics discussed: RV fridge fires. This is fascinating.