During the installation of a new commercial refrigeration system, a standing pressure test requires pressurizing the system with ____________ and allowing it to sit for 24 hours.

The correct answer is nitrogen because it is the standard choice for pressure testing refrigeration systems. Nitrogen is an inert gas that does not react with the components of the system, making it safe to use for pressurization. During the standing pressure test, the system is pressurized with nitrogen to check for leaks without the risk of damaging the system or creating hazardous conditions, which could occur with refrigerants or other gases.

Using nitrogen also allows for a clear assessment of pressure drops over time, indicating whether there are any leaks in the system. Moreover, nitrogen is readily available and comparatively inexpensive, making it a practical choice for technicians in the field.

In contrast, refrigerant, while it is a primary working fluid in cooling systems, is not suitable for pressure testing due to its potential to vaporize and create pressure fluctuations that could mask leak detection. Using air can introduce moisture into the system, leading to corrosion or other issues. Helium, although useful for some leak detection applications, is not commonly used for pressurizing entire systems due to its cost and the difficulty in handling.