What condition must be measured before performing a recovery evacuation?

The correct choice relates to understanding the guidelines for performing a recovery evacuation, particularly the evacuation level based on charge. Before initiating recovery, it is crucial to measure the amount of refrigerant that is present in the system. This measurement allows technicians to determine the appropriate evacuation level required to safely and effectively remove the remaining refrigerant.

When the evacuation level is based on the charge, the technician can ensure that all refrigerant—liquid and vapor—is adequately removed. This is in alignment with regulations and safe handling practices, preventing potential environmental damage from residual refrigerants.

In contrast, while ambient temperature, system age, and oil content in refrigerant can be relevant in various contexts, they are not primary factors that need direct measurement before a recovery evacuation. Ambient temperature can affect recovery rates and the state of the refrigerant, but it does not dictate the evacuation procedure. System age might inform how a system is treated, but it doesn't directly determine evacuation protocols. Lastly, oil content is important for understanding potential contamination but is not a condition that must be specifically measured before performing the evacuation.