Propane Style
The propane style refrigerator (more accurately called an ammonia absorption refrigerator) uses heat to operate. This means it can operate on a propane flame, but also means that when being operated on 120 volt AC or 12 volt DC, these power sources also have to generate heat. On 120 volt this is only a 1 to 3 amp draw, depending on the size of the refrigerator. On the 12 volt side, however, the amperage draw jumps to between 8 to 23 amps. The refrigerator should be run on 12 volt only when the vehicle is running and charging the battery.

An ammonia absorption refrigerator has to be level any time it is in operation and stationary. It also requires a fairly sophisticated ventilation system to expel heat from the cooling unit. If either of these two conditions are not met, the cooling unit may become permanently damaged.

AC/DC Compressor Style
The AC/DC compressor refrigerator can be run up to 30 out of level and requires only minimal ventilation. Operating on 120 volt, it will pull between 0.4 and 0.975 amps, depending on the size of the refrigerator. The 12 volt amp range is between 3.5 and 6.0 amps. This style refrigerator, which uses a motor, can only be operated on electricity, not propane.

Then Why?
Why do probably more than 95% of RVs come with the propane style refrigerator, when they are so inefficient on 12 volt and so temperamental? The answer is: propane. With standard propane tanks, an RV with a propane refrigerator can go for weeks without the benefit of any hook ups. The AC/DC compressor style, although much more efficient on 12 volt than the propane style, will barely last 24 hours with a standard battery, without recharging the battery. To be truly independent of outside power the RV would have to have a lot of batteries or some means to constantly charge (in a significant way) a few batteries.

There is a definite need, however, for the AC/DC compressor style. Any situation where the proper ventilation requirements for a propane refrigerator can't be implemented (such as many boats) is a perfect candidate. If 12 volt is going to be the only or main power source, then the AC/DC compressor style is the only way to go. If it is known that propane will never be considered as a power source, then there is no reason to put up with the requirements of a propane refrigerator.