If you are thinking of adding a small refrigerator to your popup camper or small RV, you have a variety of choices. The most common type of pop up camper refrigerator used is the "3 way" refrigerator, but for some, there might be more economical options.
These are often called "3-way" refrigerators since they can run on 120 volt AC current, 12 volts DC, or propane. It seems odd that one can make the refrigerator cold by burning gas, but the use of propane is the most efficient way to run such a refrigerator. The heat from a very small propane flame is used to boil a liquid (usually ammonia) in a closed system. Through the miracle of thermodynamics, the resulting vapor takes on heat during the process of re-condensing. It takes this heat from the inside of the refrigerator, and the result is that the inside becomes cold. This whole process uses a very small amount of propane. If the propane is used for only the refrigerator, a 20-pound tank will generally last almost a month of continuous operation.
The next best way to use the 3-way fridge is with 120 volt AC power. The electricity is used to provide the heat. If you're camping with hookups, you've already paid for the electricity, so you may as well use it instead of your gas.
The least efficient way to use the 3-way fridge is with 12 volt DC power. You should never run the refrigerator from 12 volts when camping without hookups. You will quickly run down the battery, in a matter of hours. If you don't have hookups, then you should either use propane, or turn off the refrigerator. The purpose of the 12 volt connection is to keep the contents of the refrigerator cold while traveling. You should only use this option when the trailer is hooked up to the tow vehicle, and only if you have a 12-volt charge line hooked up to the vehicle. Unless you specially requested it (and paid extra), you probably don't have this connection with your normal tail light hookup. Again, if you don't have this special connection installed, you'll quickly run down the trailer's battery.
Some people turn on their RV refrigerator and think that it's not working, because it doesn't make any noise. Your three way refrigerator will not make any noise when operating properly. Unlike the big refrigerator at home, your RV refrigerator has no moving parts. It operates under a different principle, and does not have a motor and compressor. When you turn it on, it won't do anything immediately or make any noise. It will take some time to determine whether it is working properly. The first sign that it is working properly is that you will be able to feel warmth near the vent outside, from the refrigerator's "works." You'll be able to detect this warmth before you can detect the inside cooling off. Of course, after a while, you will be able to feel that the "fins" in the back of the refrigerator are getting cold, since this is what keeps the food cold.
Some people also believe that the refrigerator is not working because they fill it up with warm food, and the food is still warm after a few hours. If you fill a refrigerator with warm food, it will take a long time to cool everything off. You rarely fill your home refrigerator with warm food. Even if you put something in there warm, the rest of the food is already cold, and the temperature will cool off relatively fast. You need to treat your RV refrigerator the same way. You can add a few items that aren't cold, and they will cool off relatively fast. But if everything starts off warm, it will take a long time for everything to cool off.
The refrigerator shown above, and other small RV refrigerators generally don't have a thermostat. Your home refrigerator has a thermostat. When the temperature inside warms up, the thermostat turns on the motor and compressor, and you hear the familiar noise of the refrigerator "running." When the inside cools off, the thermostat shuts everything off. Your home refrigerator has only two states: Either it is running at "full blast", or else it is shut off. Since the RV refrigerator has no thermostat, it is running all the time. But since it needs to work harder in the summer than in the winter, it is up to you to set the adjustment yourself. Unlike your home refrigerator, it's not necessary to run an RV refrigerator at "full blast." In the summer, you need to turn it up high. In cooler weather, you need to turn it down lower, to prevent the food from freezing.
This might seem like a nuisance, but it isn't difficult. After a few uses, you'll know where you have to set the knob for different weather conditions. If the weather changes drastically, you might need to adjust the setting. If you notice that the food is too warm, you need to turn up the setting. If you notice that the food is too cold, you will turn it down. Unless there's a drastic change in temperature, it's rarely necessary to change the setting during a trip.
The advantage of not having a thermostat is that you can run your 3-way refrigerator with absolutly no electric power. If you don't have hookups and your camper doesn't have a battery, you can still use the refrigerator.
Larger RV's often have a larger refrigerator like one of the following:
When refrigerators get this large, it is impractical to run them on 12 volts, even when in transit. Therefore, this model is a "2-way" refrigerator, since it will run on propane or 120 volts, but not 12 volts. Most of these larger refrigerators have a thermostat, however, which means that they need some electricity to operate, even when running on propane. Therefore, if you don't have hookups, you need both a battery and propane to operate it.
As you can see, 3-way refrigerators are relatively expensive. They should last many years if well maintained, but for those who camp only occasionally, the investment might be too great. There are alternatives.
The most inexpensive alternative, of course, is to simply store your food in a cooler and buy ice when needed. But there are two other options.
If you usually camp with electric hookups, then it's not really necessary to have the propane option. Therefore, you can simply use a small "dorm" refrigerator. With some ingenuity, you can mount it permanently in the camper. Or, if you prefer, you can carry it separately and put it in a convenient spot when you set up camp. To get an idea of what is available, here are some Compact Refrigerators on Amazon. Some of these refrigerators have a compressor like your larger one at home, and will make a small amount of noise. These are generally more efficient than the other type, which operate under a thermoelectric principle. Generally, the thermoelectric models are less expensive and lighter, however. Using one of these compact refrigerators can be a very economical way to add a refrigerator if you camp with electric power.
These small refrigerators can often be found on sale during "back to school" sales. Here are examples of some relatively inexpensive models:
Another option that some people consider is the "12 volt cooler". These look like traditional coolers, but they can be plugged in to a car's 12 volt socket. They are relatively inexpensive. For example, here is a large selection of 12 Volt Coolers on Amazon.
While one of these coolers might work well for some, they're not a good option for long-term use. They draw quite a bit of electricity, and will run down a battery quite fast. If that's the battery of your tow vehicle, then you might discover that the cooler was a big problem! Also, these units do not cool very effectively. They are fairly good for keeping food cold. But they're probably not up to the task of chilling items that are not already cold. One of these coolers is a very good option if you use it while driving, because the vehicle will keep the battery charged. But this type of cooler is not suitable for leaving plugged in overnight. Some of these coolers, however, will run from 120 volts. So if you have hookups, they might be helpful, especially if you want to use the same cooler while driving around. However, they are generally less efficient than "dorm fridges," and the dorm fridge will generally be less expensive. So if you plan to use them on 120 volts exclusively, they're probably not the best option.
If one of these will fit your needs, here are some examples of available models: