A unitary air conditioning system must be?

A unitary air conditioning system must be charged before installation to ensure optimal performance and efficiency. When the system is charged, it refers to filling it with the refrigerant required for it to operate correctly. Proper refrigerant levels are critical because they facilitate the transfer of heat within the system, which is essential for cooling or heating spaces effectively. Without the correct charge, the unit might not cool efficiently, could freeze up, or even lead to compressor failure, significantly affecting both comfort and energy usage.

While the other options may seem plausible within different contexts, they don’t relate to the fundamental requirement of preparing a unitary air conditioning system for operational readiness. For example, installing a system without charge is not feasible since it wouldn't function properly, and running a unit continuously is not a requirement but rather a consideration based on the cooling needs and efficiency measures. Additionally, while being listed under various standards is important for safety and compliance, it does not pertain to the initial requirements for the system to be installation-ready.