This has been asked many times - even by myself at one time on a planet long, long time ago... Let me see if I can better explain...
A gas refrigerator uses ammonia as the coolant, and it uses water, ammonia and hydrogen gas to create a continuous cycle for the ammonia. The refrigerator has five main parts:
Generator - generates ammonia gas
Separator - separates ammonia gas from water
Condenser - where hot ammonia gas is cooled and condensed to create liquid ammonia
Evaporator - where liquid ammonia evaporates to create cold temperatures inside the refrigerator
Absorber - absorbs the ammonia gas in water
The cycle works like this:
Heat is applied to the generator. The heat comes from burning something like gas, propane or kerosene.
In the generator is a solution of ammonia and water. The heat raises the temperature of the solution to the boiling point of the ammonia.
The boiling solution flows to the separator. In the separator, the water separates from the ammonia gas.
The ammonia gas flows upward to the condenser. The condenser is composed of metal coils and fins that allow the ammonia gas to dissipate its heat and condense into a liquid.
The liquid ammonia makes its way to the evaporator, where it mixes with hydrogen gas and evaporates, producing cold temperatures inside the refrigerator.
The ammonia and hydrogen gases flow to the absorber. Here, the water that has collected in the separator is mixed with the ammonia and hydrogen gases.
The ammonia forms a solution with the water and releases the hydrogen gas, which flows back to the evaporator. The ammonia-and-water solution flows toward the generator to repeat the cycle.
And that's how it works...