HVAC - EPA Certification Practice Exam

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During vacuum testing, what indicates a leak check is necessary according to ASHRAE guidelines?

System reaches 5mm Hg
Pressure rises above 2.5mm Hg
Temperature exceeds 130 degrees
Vapor pressure drops below 1 inch Hg

The correct answer is: Pressure rises above 2.5mm Hg

In the context of vacuum testing as outlined by ASHRAE guidelines, a pressure rise above a specific value serves as an indicator that a leak check is necessary. When the system experiences a rise in pressure above 2.5 mm Hg during vacuum testing, it suggests that the integrity of the system may be compromised. A stable vacuum is essential for ensuring that there are no leaks present, as even tiny leaks can allow moisture and air to enter the system, leading to issues in performance and efficiency. The gauge used for measuring vacuum does not indicate a problem at lower thresholds, and remaining below this threshold is crucial for confirming a successful vacuum. By having a pressure rise above 2.5 mm Hg, technicians have a clear signal that further investigation is warranted to ensure the system can operate effectively without contamination that could adversely affect its performance and longevity.