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 choice is nitrogen, which is commonly used for standing pressure tests in refrigeration systems. Nitrogen is an inert gas, meaning it does not react chemically with the materials of the refrigeration system, making it a safe option to pressurize the system during testing.

Using nitrogen allows technicians to effectively check for leaks without the risks associated with using refrigerants or other gases. It enables them to pressurize the system without adding any burdens of contamination or damage that could occur from using refrigerants. Furthermore, nitrogen is readily available, cost-effective, and leaves no moisture or residues that could jeopardize the integrity of the refrigeration system.

Additionally, a 24-hour testing duration helps ensure that any minor leaks can be detected, as even small amounts of escaping gas would result in a measurable drop in the pressure over that time. Therefore, nitrogen is the best choice for maintaining system integrity and safety during installation.