Why moisture effect in refrigerator cooling system ?

Moisture combines in varying degrees with the most commonly used refrigerants. This mixture reacts with lubricating oil and other materials in the system, to produce highly corrosive compounds. As a result of chemical reactions often leads to pitting and other damage to the valves, seals, bearing journals, cylinder walls and other polished surfaces in the system. It can also degrade the lubricant oils, sludge that may stick together valves, hammer oil passages, evaluation of the bearing surface and produce other effects which reduce the life of the system.