HVAC Contractor Practice Exam 2025 - Free HVAC Practice Questions and Study Guide

In the context of performing a nitrogen pressure test on a refrigerant piping system, particularly for units over 20 tons, the recommended duration for the test to remain active is 24 hours. This extended period is critical for ensuring the integrity of the system under pressure and allows for adequate time to detect any potential leaks.

During the nitrogen pressure test, the piping system is filled with nitrogen gas at a specified pressure, typically around 150 psig (pounds per square inch gauge). The primary aim of this test is to verify that the piping system can maintain that pressure without any drop, which would indicate a leak.

The reason for the 24-hour duration is to provide sufficient time for the gas to equalize and settle, which can offer a more accurate assessment of any slow leaks that may not be immediately evident in a shorter testing period. Additionally, this length of time aligns with best practices and standards set within the industry, emphasizing thoroughness and reliability in refrigeration system integrity testing.

Shorter test durations, such as 1 hour or even 6 hours, might not be sufficient to catch subtle leaks or pressure changes, while a 12-hour test may not provide the comprehensive assurance that a careful installation and inspection process demands, particularly in larger systems where