EPA Type 2 Practice Test

During evacuation of a system that contains a lot of water, the rapid drop in pressure can cause remaining water to cool and freeze inside hidden pockets or crevices. Ice in those trapped areas can form plugs that block vents and valves, making the evacuation hard or impossible. Introducing dry nitrogen acts as a purge gas: it displaces air and moisture, delivering a dry, inert gas through the system. By reducing the amount of water vapor and keeping the environment dry, the conditions that would lead to freezing are minimized. This helps prevent ice plugs from forming and keeps the evacuation process smoother. The other issues—condensation in lines, overheating, or foaming oil—don’t address the specific problem of ice formation from trapped water during a vacuum purge, which is why using nitrogen to purge and dry the system is the best approach.