Hello, Dave,
I have a general question. I always ensure my rig is level after we arrive at a campsite prior to turning on our absorption refrigerator. (No, we do not run it while driving.) For those folks that do run their absorption fridge while driving, up and down mountains, rough roads, curves, etc., what are the impacts to the efficiency and safety aspects of the fridge? It seems counterintuitive to have this type of fridge jostled around and not level while driving. Thanks. —Gary, 2021 Jayco Melbourne 24L
Hi, Gary,
The advantage of an absorption refrigerator is there are no moving parts so it can take the jostling you have described as well as the potholes of the Midwest better than residential models. Plus, it can handle storage in -20 degree weather and sweltering heat.
How an absorption refrigerator works
Let’s take a look at how the absorption refrigerator works and what happens when driving and not being level.
Here is a diagram of both the Dometic and Norcold models, which operate similarly. A rich solution of hydrogen, ammonia, water, and sodium chromate for lubrication are stored in the absorber vessel. The solution flows down the liquid heat exchanger to the burner assembly, which heats the solution either with a flame on LP or heating element on 120-volt power.
The ammonia turns to a vapor and travels up to the condenser fins at the very top and then through the freezer evaporator, where it flashes and removes heat. It goes through a series of chemical reactions and changing from a vapor back to a liquid through the refrigerator evaporator. All this flows back down to the absorber vessel to cycle again through the cooling unit tubes by gravity.
Being level while camping
It is important to have the unit level while camping so the fluids can flow through the tubes by gravity. According to the Norcold Service Manual, the unit must be level 6 degrees front to back and 3 degrees side to side. Both Norcold and Dometic provide a bubble level that can be placed in the freezer compartment to verify proper leveling.
If the unit is out of level, the angle of the cooling unit tube will be drastic and the solution will “pool” at a corner and get hot, eventually causing flaking, which will restrict the flow and affect cooling efficiency.
According to the Norcold Service Manual: Exceeding the maximum off-level limits can permanently damage the cooling unit. The cooling unit or its performance are not affected when the vehicle is in motion.
Driving with the refrigerator running
First, I do not advise running the absorption refrigerator on the propane mode while driving as your rig will have an open line of propane and a flame at the burner assembly. This is not only dangerous if the propane system develops a leak, but also when entering a fueling station!
There are some alternatives, including just keeping the door closed. I have conducted tests on both the Norcold and Dometic models bringing the unit down to 36 degrees, shutting off the RV refrigerator, and measuring inside temperatures every hour. Both will maintain close to 40 degrees or below for over 6 hours with a 5 lb. bag of ice in the freezer section and modest food in the refrigerator compartment.
Notice the 43 degrees is 6 hours later and the ambient temperature inside the rig was 91 degrees!
Another option
Another option would be to run the refrigerator on 120-volt power by using an onboard generator or through an inverter and battery power. While you are driving, the engine alternator will provide a charge through the Battery Isolation Management (BIM) solenoid and keep the house batteries charged which can provide power to an inverter and 120-volt power to the refrigerator. Check your alternator to verify it has enough amp capacity to also charge the house batteries.
Notice the statement in the Norcold Service Manual: The cooling unit or its performance are not affected when the vehicle is in motion.
Since there are no moving parts, jostling and road vibration will not affect the performance of the cooling unit and other components. In fact, it most likely will help move the fluid through the cooling unit tubes. Most RV trips do not have long driving periods that would cause it to be out of level for hours.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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I’ve always been amused to see that many of the same people who bemoan the poor build quality of today’s RVs also insist that there is little danger in driving with the propane on. Seems nuts to me.
We’ve done many 8-hour travel days during summer >100 degree “heat bombs” with the fridge off with no problems. The units are impressively well insulated and your food will stay cool. If in doubt, add some ice before going.
Thank you, Dave! These absorption refrigerators are interesting devices. Seems rather creative to use a heating source to create cooling. Safe travels! 🙂
A three-way fridge can run on 12 volts from vehicle system.
We always drive with the propane off and the refrigerator running on 120V AC. Easy to do with a motor home, 200-amp alternator, and inverter. Towing can be more challenging if needing to arrive at the campsite with fully charged batteries.
Circulation in ammonia fridges is complicated. Blockage mostly occurs in the “absorber” just before the boiler. ARP https://www.arprv.com/ has done measurements while RVs are in motion. They found blockage and dangerous overheating on steep grades.
This led to the development of the “Fridge Defend” safety device. I have had one for 4 years and like it. Here is my installation notebook, a Google Doc: http://bit.ly/2Qyw9Ac
You are always on here trying to sell your product and trying the “scare” point. How about paying this swell site instead?
I think you’re jumping to incorrect conclusions, “Joyce M.” On the link for John’s installation procedure, it very clearly states, in part: “CAUTION: This is the personal but shared “laboratory notebook” of an independent user and hobbyist. It is a living document that will evolve as operational experience is gained. The writer is not affiliated with or endorsed by any company mentioned, and products were purchased at retail….” Also, John’s full name does not come close to matching the names on the ARP website, which reads, in part, regarding the company owners: “Paul and Mao Unmack are practitioners of engineering science that have committed themselves to RV safety. We are not sales people, we do not push product you do not need. We at Fridge Defend hold paramount the safety, health, and welfare of the public. This website is presented only in an objective and truthful manner and is based on sharing our extensive RV experience….” Here’s a link to their About Us page. Maybe John is just a very satisfied customer and believes in this product. Oh, BTW. John has commented 11 times over the past year and this is his only comment regarding the Fridge Defend. Have a good night. 🙂 –Diane at RVtravel.com
We keep the door closed and rely on frozen ice packs to help keep the refrigerator portion cold while in motion. That said, we are not disconnected for more 6-7 hours on a travel day.
Whatever you are comfortable with…..All my rigs in the past 40 years with Norcolds I’ve run with them keeping my ales and ice cream cold with the fridge on all the time. , Drive all day in hot weather, Grabe an Ice Cream bar when landed and after getting set up and relaxing, a swell ice cold glass and an Obsidian Stout…..Floats my boat!