Final answer:
Oxygen should never be used to pressurize a system because it can react explosively with certain refrigerants, it supports combustion, and can cause corrosion within the system. Inert gases like nitrogen are preferable for pressurization due to their lack of reactivity and the reduced hazard they pose.
Step-by-step explanation:
Oxygen or compressed air should never be used to pressurize a system because it may react explosively with certain refrigerants. When oxygen comes into contact with certain refrigerants under pressure, there is a risk of a chemical reaction that can result in an explosion, posing a significant safety hazard. Moreover, oxygen supports combustion, and when it is used in systems with oils or other combustible materials, there is an increased risk of fire or explosion.
Compressed oxygen is not only a hazard due to its reactivity but also it poses threats of corrosion to a system. This characteristic can lead to the deterioration of metal components, potentially causing leaks or system failures. For pressurization purposes, other gases like nitrogen are preferred because they are inert and do not pose these dangers. Likewise, the use of carbon dioxide in systems can be advantageous due to its non-reactivity and other benefits under specific conditions.