RV Maintenance: Absorption Refrigerators

Graphic showing components of refrigerator cooling system
Illustration: Rob Roy

Best practices for keeping your RV’s absorption fridge running smoothly. 

RV owners are dependent on their refrigerators. In fact, not only is a refrigerator necessary for self-containment, most owners would probably cancel their trip plans if it quit working. It’s easy to think that an RV refrigerator will be ready to go and be just as reliable as a residential version, but there are a number of issues that are exclusive to absorption refrigerators. Repairs, and possible replacement, are costly — to the tune of hundreds or even thousands of dollars.

Following are five of the most common practices that can cause an RV refrigerator to fail. As with most RV systems, reading the owner’s manual and becoming familiar with the appliance will go a long way toward preventing a chilled-food calamity.

DON’T: Operate the refrigerator too far off level

An RV absorption refrigerator is dependent on heat and the proper flow of its refrigerant. Unlike a residential fridge that uses one chemical for refrigeration, an RV version uses a solution of ammonia, hydrogen, water and sodium chromate, which is heated to the boiling point and then cooled to absorb heat from the food-storage areas. Heat is provided by an electric element or an LP-gas flame.

This design is ages old and was commonly used before the advent of electric compressors and modern refrigerants. However, physics has a lot to do with its proper operation, and while the cooling-unit design has been fine-tuned over the years, it’s still dependent on being “comfortably” level to operate properly, with tolerances of 3 degrees side to side and 6 degrees front to back.

If the refrigerator is operated off level, then the heating of the boiler is uneven, creating hot spots where the sodium chromate can begin to precipitate out of the solution and form crystals or flakes in the solution. Once formed, the flakes always remain and can create a blockage. Once the blockage forms, the cooling unit becomes damaged and must be replaced at considerable expense.

Preventing this malady can be accomplished simply by leveling the RV to a comfortable position. A proper posture requires that the floor of the freezer be relatively level. This can be checked with a small bubble level. It may not be possible to achieve a perfect position, but if the bubble in the level is half in the center bull’s-eye, the refrigerator will likely perform properly.

Tech Tip

It’s best to turn the refrigerator off when parking temporarily on an unlevel surface, such as while shopping or sightseeing.


Graphic of refrigerator tilting side to sideLevel Best

For the refrigerator to operate properly and avoid damage, it must be in a comfortably level position — within 3 degrees side to side and 6 degrees front to back. A bubble level set on the freezer compartment floor is the best place to check refrigerator attitude. When the boiler isn’t level, the coolant can be overheated, which causes the sodium chromate to precipitate into flakes and eventually leads to a blockage. The same thing can happen if the refrigerator is used in ambient temperatures below 25 degrees Fahrenheit.


DON’T: Use the refrigerator in severely cold temperatures

In the past, not too many people used their RV in arctic or below-freezing conditions, so the operation of the refrigerator was never considered. However, in recent years, manufacturers have been building four-season-capable RVs, based on a demand from RVers who want to extend their adventures into the winter cold. Unfortunately, RV refrigerators aren’t built to handle this well.

According to Dometic, a major supplier of absorption refrigerators to the RV industry, in temperatures below 25 degrees Fahrenheit, the refrigerant may get so cold that it can begin to “gel up and not flow through the coils as intended.” Heat applied to the gelled refrigerant will be uneven (much like when running in an unlevel condition) and can solidify, damaging the cooling unit. As a result, the company advises customers not to use the refrigerator when it’s below 25 degrees outside, let alone in subzero temperatures.

Dometic refrigerators have a low-ambient temperature control that helps them continue operating in cold conditions, but not below the aforementioned temperatures. The difficulty here is maintaining ventilation to the cooling unit while keeping it warm enough to operate. An absorption cooling unit requires free-flowing air, as well as ventilation for the propane-fired boiler, which is why there are vents on the outside walls and roof for the refrigerator. Close the circulation off, and not only will the cooling unit “suffocate” and not work properly, but there would be a hazard from the propane flame and carbon-monoxide exposure.

Tech Tip

If you must consistently operate a refrigerator in icy conditions, a compressor-powered refrigerator may be more desirable.


DO: Make sure the house batteries are properly maintained

The very foundation of any RV’s electrical system is the battery bank. RVs are built with a 12-volt DC (direct current) electrical system that powers the lighting, ignitors, circuit boards and so on. An RV refrigerator will not run without 12-volt DC power, even when plugged into an electrical hookup. And, as with any RV appliance that malfunctions, diagnosis always begins by verifying that the energy sources are correct, including propane pressure and the proper electrical voltage.

Many RV owners, especially those who leave their RVs parked on seasonal or permanent campsites, ignore the batteries and sometimes disconnect them altogether. If the power should go out in the park, especially when you’re not there, the result can be a biological disaster inside the refrigerator that can result in a total replacement. No matter what you do, the smell will likely remain.

It’s best to maintain (with proper conditioning) at least one or two house batteries at all times. If they are flooded lead-acid batteries, check the distilled-water level frequently and make sure the charger is working correctly. That way, if the electricity in the campground goes out, the power for the refrigerator’s circuit boards will remain on, allowing the unit to switch from AC to LP-gas, for instance, and to run for many hours while the power is out. Even a temporary lapse in DC power will cause the fridge to shut down, and once it does, it will not restart automatically when power is restored. This feature is actually a good thing; that way, should food thaw and spoil, you’ll know right away.

Tech Tip

A great way to make sure food is safe is to use a refrigerator thermometer that records high and low temperatures, like those available at Camping World.

Chris Dougherty maintaining an RV refrigerator.
An RV refrigerator requires 12-volt DC, 120-volt AC or LP-gas to heat the cooling unit, and 12-volt DC to operate the electronics at all times. Having the correct gas pressure and electrical supply coming in are essential for proper operation.

DO: Make sure the refrigerator is properly ventilated

As previously mentioned, ventilation is the name of the game with absorption refrigerators. To meet the ventilation requirements, the refrigerator cabinet should have been designed specifically for the refrigerator. The tolerances for space on the sides, top and rear of the fridge are exacting for proper operation. If the spacing and baffling of an RV refrigerator are done improperly by the RV manufacturer, performance issues can occur.

Ventilation of the refrigerator can be affected by many factors, some being more obvious than others. The side and roof vents are sized and placed specifically for the model of refrigerator. These specifications may need modifying if a different model is installed. The baffling in the back is also essential to maintain airflow. The outside vents must never be blocked. Common blockages range from a tarp or RV cover to wasp nests and piled-up leaves. It’s not uncommon to see people block off the side-vent openings on RV refrigerators in cold weather, which not only can suffocate the unit but can be dangerous.

Tech Tip

If the refrigerator is not operating properly in hot weather, consider adding a fan kit to the back side.

Chris Dougherty wiping the empty shelf of an RV refrigerator.
Once the refrigerator is empty, wipe down surfaces with Clorox wipes or a similar cleaner.

Do: Maintain the refrigerator as recommended by the manufacturer

Refrigerator maintenance is outlined in the owner’s manual, but most folks never read it. Most of the maintenance is pretty simple, but failing to do it can shorten the life of the refrigerator.

Keeping the interior and back of the refrigerator clean is very important. The plastics inside the fridge can hold odors and can get grungy over time, but the real issues are mold and mildew, which can be health hazards. When the trip is over, empty the refrigerator, turn it off and clean the interior with Clorox wipes. Leave the doors open so it can defrost and dry. Once everything is dry, secure the doors using the hold-open locks.

The rear of the refrigerator is open to the outside, so make sure the vent openings are clear of all debris, nests and excessive dirt. Check the burner housing for excessive rust, and vacuum out (with the flame off) as needed. Excessive rust, especially on the burner, warrants a professional inspection.

Lastly, it’s essential to make sure the LP-gas regulator is functioning correctly. This can only be done using a manometer by a propane-gas or RV technician.

An RV absorption refrigerator is an expensive appliance that no one wants to replace arbitrarily. However, its ability to function properly requires proper maintenance. Doing so will keep your vittles nicely chilled — and safe to eat. Operational situations that cannot be resolved must be checked by a certified technician, but there’s still plenty you can do to ensure greater longevity.

Tech Tip

Spraying a fine mist of a bleach-and-water solution on the inside surfaces of the refrigerator will help prevent mildew.

Dirt and rust on an RV refrigerator.
Left: There’s a lot of dirt around the back of this refrigerator, but the burner and ignitor are nice and clean, and the gap is correct. Right: The production of rust is typical for a boiler tube that is used frequently (think barbecue grill). The rust must be removed to make sure it doesn’t plug the burner.

Chris DoughertyChris-Dougherty-headshot is technical editor of Trailer Life and MotorHome. Chris is an RVDA/RVIA certified technician and a lifelong RVer, including 10 years living full time in an RV. He and his wife make their home in Massachusetts and hit the road in their heavy-duty truck towing their travel trailer every chance they get.


3 COMMENTS

  1. at the beginning of the season i learned to take compressed air (computer air with a red hose) and blow out all the access ports and holes. it works every time. before i figured this out the fridge would not light.

  2. If I am traveling in the mountains and generally off level when driving to a from destinations, is my fridge at risk?

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