During evacuation of a system containing large amounts of moisture, which gas is typically used to prevent freezing by increasing pressure?

The use of nitrogen during the evacuation of a refrigeration or air conditioning system containing substantial moisture is a common practice primarily because it serves to prevent freezing within the system. When moisture is present, the lower temperatures encountered during the evacuation process can lead to the formation of ice, potentially causing blockages or damage to components.

By introducing nitrogen into the system, which is an inert gas, the pressure inside the system is increased. This elevated pressure raises the boiling point of moisture and prevents it from freezing. Thus, nitrogen helps to maintain a higher temperature around the moisture, allowing for more effective evacuation without the risk of ice formation.

Utilizing nitrogen is also advantageous because it doesn't react with any of the materials used in the system, ensuring that the integrity of the components is maintained throughout the evacuation process. This makes nitrogen an ideal choice in situations where it's critical to manage moisture effectively while preserving system functionality.

In contrast, carbon dioxide, helium, and argon do not provide the same benefits in this context, either because they do not effectively increase pressure in a way that mitigates freezing or because their chemical properties might not align with the needs of the evacuation process.