If you own an RV, you’ve probably used the refrigerator inside to keep food and drinks cool for your trip. It can be a wonderful convenience to have access to essentials like sandwich meats, cheese, condiments, eggs, milk, or even just a cold soda for a lazy Saturday without having to keep a cooler full of ice for the duration of your trip.
But have you ever wondered how an RV refrigerator works? It is actually pretty different from how residential refrigerators work (although home fridges are now available on newer RVs) and are designed to run more efficiently so they can be run off of a generator, shore power, propane, or even DC power from your battery.
In this article, we’ll go over how an RV refrigerator works and how it differs from a residential refrigerator.
Generally speaking, there are three types of refrigerators in RVs nowadays: two-way, three-way, and residential fridges.
Two-way fridges are still the most common in RVs, and until relatively recently they were the only option. These appliances can be powered with AC electricity (from shore power or a generator) or propane.
A three-way fridge can use both of those power sources as well as 12V DC electricity, so you can run your RV’s refrigerator with just a battery. While this can work while the RV isn’t running, it will drain the battery pretty quickly, so you should typically only use this in a motorhome (not a trailer) while the engine is running and charging the battery.
Both two-way and three-way refrigerators work with absorption technology, whereas residential refrigerators, like the one in your home kitchen, use a compressor. Residential fridges are great in a stationary location, but they have a lot of moving parts, making them less than ideal for use on a highway. Residential refrigerators also take up more electricity, which is fine for the high-capacity fridges in houses, but not necessary for the amount of food you’ll typically need in an RV.
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Absorption refrigerators use either a propane flame or an electrical heating element to heat chemicals up, which cool the inside of the refrigerator through a complex combination of chemistry and physics.
When an absorption refrigerator starts, it has a solution of liquid ammonia and water in a tank, which is then heated by whichever power source the refrigerator is using. Since ammonia has a lower boiling point, it evaporates away from the water and goes up into the condenser, while the water flows into the absorber.
The condenser absorbs the heat from the ammonia, dissipating it to the outside environment, cooling and compressing the ammonia back into a high-pressure liquid. This liquid then goes through an expansion valve, which reduces the pressure and in turn temperature of the ammonia (in a closed system like this where the ammonia never leaves the tubing and the volume of the tubes stay the same, the pressure of the fluid is directly proportional to its temperature) resulting in a cold, low-pressure liquid.
The now-cooled liquid ammonia then passes through an evaporator. There, the heat from inside the fridge is absorbed by the liquid ammonia in the evaporator, cooling the inside of the fridge. This heating turns the ammonia back into a gas which can flow back into the absorber to dissolve into the water, allowing the cycle to start again.
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This is a great solution for cooling in an RV because it has no need for moving parts and just uses the physics of evaporation and condensation to effectively suck the heat out of the fridge.
Compressor refrigerators can reach much lower temperatures and stay more consistent and allow you to freeze food long term. But if you intend to travel a lot and keep food cool on the road, absorption refrigerators are the way to go. As long as the fridge itself is well-insulated and the interior of your RV stays at a moderate temperature, you shouldn’t need to run your fridge all that much.
If you tend to use your RV for longer periods, especially while connected to shore power at a campsite or RV park, then you might want to consider a residential-style compressor fridge.
The process of a compressor fridge relies on many of the same processes. The main difference is that instead of using an electrical heating element or flame from LP gas to heat and separate an ammonia solution, a compressor fridge uses one fluid throughout the whole system and uses motorized fans to aid in heat exchange.
A vapor goes through a compressor, increasing the temperature and superheating the gas. That gas then goes into a condenser where it is cooled down by a fan blowing external air until it is a high-pressure liquid. It then passes through an expansion valve which reduces the pressure (and therefore the temperature) and sends that cold liquid to the evaporator. Another fan then actively pumps the air out from the interior of the refrigerator to the evaporator, heating the liquid into a high-pressure vapor, and cooling the inside of the fridge. This pressurized vapor then goes back to the compressor, starting the process over.
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This method of refrigerating can provide great results with very low temperatures, and very consistent cooling. However, there can be drawbacks to this in an RV. First is that the motors used to drive the fans in the condenser and evaporator can be very draining on the battery if used with an inverter, or it can take up a lot of the energy from the generator or shore power.
In an RV with a 50 amp electrical system, this should be no issue since a residential refrigerator needs up to 800 watts to run, which is only a small fraction of the 12,000 watts available. But in a 30 amp RV, you only have 3,600 watts to work with, so you would be much better off with the 200 watts needed to run an absorption fridge; especially if you want to run the air conditioning or water heater as well.
A residential refrigerator also removes the option of running on propane. And if you want to run the fridge while on the road, there is more risk of causing damage to the moving fans from bumps on the road than using the heating element of a two-way or three-way fridge. So absorption fridges are ideal for the RVer on the go, while residential refrigerators are great for your home base.
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