When is it acceptable for appliances to not be evacuated to the prescribed level?

The correct answer is grounded in the practical realities of servicing refrigeration systems. It is understood within HVAC practices that evacuating an appliance to the prescribed level is crucial for ensuring that moisture and non-condensables are removed, which enhances system performance and longevity.

However, there are situations where achieving the required evacuation level is not feasible due to leaks. If an appliance has significant leaks, it may introduce air and moisture during the evacuation process, which can render it impossible to achieve the necessary vacuum level. In such cases, continuing to try to evacuate the system to the required level could be futile and counterproductive, leading potentially to further complications if the system is operated without repairs.

The other options are less viable. For example, new appliances generally do not require evacuation unless they have been contaminated. The absence of leaks does not exempt a system from being evacuated, as proper procedure must always be followed regardless of leak status. Lastly, a technician's subjective judgment does not determine the need for proper evacuation levels; industry standards dictate these procedures for safety and efficiency. Therefore, the scenario of being unable to attain prescribed evacuation due to existing leaks is the only acceptable reason for not following the mandated evacuation procedures.