A gas fridge uses heat to cycle the refrigerant through the absorption cooling system. LPG gas is the most efficient way to run an absorption fridge, as the LPG gas instantly produces a very hot flame.
240V power will also cool an absorption fridge well, although the heating element needs to produce the same amount of heat as a gas flame, so it is not as efficient as on LPG gas.
12 V operation in an absorption fridge is often considered a holding or travel mode only. The temperature of the fridge will remain steady, but the fridge will not have the power to cool down quickly. This occurs because the small 12 Volt heating element cannot produce the same amount of heat as a gas flame, so it uses a lot of electricity trying to keep up. A stable, level surface is required to operate an absorption fridge in the most effective way. So a moving car, caravan, motorhome or boat is not an ideal situation.
2-Way and 3-Way are terms referring to absorption fridges which can operate on 2 or 3 different power supplies. This is usually a combination of LPG Gas and 240 Volt (2-Way) or LPG Gas, 12 Volt and 240 Volt (3-Way).