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When we first bought our RV there were so many new systems to get used to and understand how they worked. An RV refrigerator works a bit differently than your standard house one so I did some research to understand how it works.
So how does an RV propane fridge work? An RV refrigerator works by absorption and a chemical reaction between ammonia, water, and hydrogen. The ammonia is heated then goes through an evaporation and condensation process which causes the cooling effect of the fridge. The ammonia is heated either by a propane flame or electric element.
This is a very basic description of the process, I’ll dig into it a little deeper, go over the different types of fridges available as well as cover some general operating information.
Table of Contents
The Full Cooling Process
An absorption fridge consists of five main parts the generator, separator, condenser, evaporator, and absorber.
The process starts off with an ammonia and water solution in the generator. This solution is heated until the ammonia reaches its boiling point.
Now the ammonia solution [L1] flows into the separator where the ammonia evaporates and separates from the water.
The water [L2] will make its way down into the absorber and the ammonia gas [L3] will rise into the condenser. Here the heat dissipates and the ammonia turns back into a liquid.
Next, the liquid ammonia [L4] goes into the evaporator where will mix with the hydrogen gas. The ammonia evaporates (again) but this time the evaporation process removes the heat from inside the fridge causing the fridge box to cool down.
The ammonia and hydrogen gas [L5] end up in the absorber where the ammonia reforms a solution with water and the hydrogen gas [L6] is now free to flow back to the evaporator.
The ammonia and water solution [L7] make their way back to the generator where the process is repeated.
During the cooling process, you’ll have noticed that the heat is applied to the ammonia and water solution in the generator in order for it to boil and evaporate. This heat will be produced by either propane or electricity.
With a propane heat source, there is an open flame that will heat the chemicals. If it’s an electric heat source it is produced by an electric element.
Two Way vs Three Way RV Fridge
In the RV world, there are two types of absorption fridges a two way or a three way.
A two way fridge allows your unit to run on either L.P. gas (propane) or 120VAC. This means that when set to “Auto” your unit will automatically switch from propane to 120VAC power when you are plugged in and back to propane when you unplug.
A three-way fridge is similar to a two way but has the added option of running on 12VDC power as well. The downside to the 12VDC is there would be a very high current draw in order to keep your icebox cold.
When switching from electric to propane a small igniter coil is signaled to spark and regulating valve opens to allow fuel to the coil. The igniter sparks the fuel and creates the flame.
When switching back to shore power (AC electric power) the regulating valve simply closes, snuffing the flame.
Keeping Your Fridge Cool
Food safety is a huge factor when it comes to fridges. I highly recommend getting a little thermometer (Amazon Link) for your fridge and freezer to make sure your food is being kept at optimum temperatures. For a fridge, this is 34-40ºF (3-5ºC ) and a freezer 0ºF (-18ºC).
Before setting out on the road you’ll want to let your fridge and freezer get to temperature. This usually takes about 24 hours before your unit is at the right temperature.
To help keep your fridge cool you can invest in a small battery operated fan (Amazon Link) to place inside the fridge cabinet. This will help the cool air circulate keeping your items cooler and reduce your refrigerator’s workload.
As much as possible, you’ll also want to put precooled items and prefrozen items in your fridge and freezer. It takes a lot less energy for your fridge to keep something cool that is already cool than to cool down something hot.
Also, you may find the temperature in your fridge will rise if you put something too warm in the fridge, which is not a good scenario. I know it’s not always possible to do this but letting your leftovers cool to room temperature before putting them in the fridge will help keep things cold.
Ambient Temperature and Your Fridge
The outside ambient temperature can also affect how well your RV fridge is functioning. The reason for this is because of your heat exchanger.
The heat exchanger is venting the hot air from the absorption process outside where it can dissipate. This becomes an issue when it’s already steamy out.
If you can strategically position your RV so the sidewall where the fridge is located is in the shade that will give your fridge a little relief when it’s already sweltering out. The lower fridge access panel is the cool air intake for the fridge ventilation. You’ll want to make sure this area is kept free of debris and blockages to keep it well vented
When it’s cooler outside you can set your fridge to a warmer setting. When it’s hotter out you’ll want to select a colder setting.
Our fridge setting ranges from 1-5, with 1 being the warmest and 5 being the coolest. This is where a thermometer comes in handy so you can monitor whether you need to adjust the temperature of your fridge.
Keeping Your RV and Fridge Level
Leveling your RV is for more than your own personal comfort. Since the fridge cooling system depends heavily on gravity, being out of level can be a big deal to your fridge. The chemicals may stop circulating if the fridge is too tilted which, at the very least, will cause the fridge to be less efficient.
How much out of level can you be? Well, up to 3 degrees should be okay or half a bubble. If you run your fridge out of level for even 30 minutes you run the risk of damaging your unit. Learn more about why your RV fridge needs to be level in our article, Why Your RV Fridge Needs to Be Level.
To learn more reasons to level your RV and how to know your level is actually showing you your rig is level I recommend reading my article, Why RV’s Need to Be Level and How to Know Your Level is Level.
Driving With Your Fridge Running
Now you might be worried about barreling down the road with an open flame. I’m not going to say that it’s perfectly safe to do this but many RVers leave their fridge running on propane. Others opt to turn off their fridge while driving.
We’ve always left our fridge running on propane while traveling and never worried about it.
If you have a three way fridge then problem solved, just set it to the 12VDC setting while you are driving.
Some worry about the level issue mentioned above while driving. But the motion of the RV keeps the chemicals moving and allows the fridge to continue to operate efficiently while traveling.
If you choose to turn off your fridge while on the road that’s perfectly fine too. You’ll only lose around 4ºF per 8 hours. So if you get your fridge super cold before setting out that’ll help keep things cool. Also, try to stay out of the fridge till you get it running again.
A word of caution, you should turn off your propane prior to entering a gas station. Open flames + fuel = bad idea
Ferries will also make you turn off your propane tanks prior to boarding.
How Much Propane Does an RV Fridge Use?
RV fridges tend to be very efficient with their use of propane. Since the absorption process is a closed loop the amount of propane needed to heat the ammonia solution is very minimal.
Propane consumption also will vary from one brand and model to the next. The smaller the unit the less fuel it will use. Newer units tend to be more efficient as well.
The average sized RV fridge is around 6 cubic feet, this will probably consume about 1-lb of propane per day. For reference, your standard BBQ tank is about 20 lbs.
One RVer stated they ran their propane fridge in “excess of 40 days (one) summer on about 8 gallons of propane”. That’s just over two BBQ tanks of propane. Not bad when you probably use more propane in your actual BBQ during the summer.
Can I replace my RV fridge with a standard mini fridge? While it’s possible to change your RV absorption fridge to a mini compressor fridge you will likely have to run new 120VAC plug for the fridge, ensure there is proper airflow around the unit (as recommended by the manufacturer), and you will be limited to only using your fridge on generator power or shore power.
Do I need electricity to run my RV fridge on propane? Even when your fridge is running on propane you will still need some power from your 12VDC system to power the circuit board of the fridge. If your house batteries are on the fritz then you will have issues running your refrigerator.
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