Answer:
Liquid charging of an R-12 refrigeration system with the risk of freezing is begun with vapor from a vacuum level to a pressure of approximately 2 PSIG.
Step-by-step explanation:
When initiating the liquid charging process in an R-12 refrigeration system where there's a risk of freezing, it's crucial to start with vapor. This prevents potential issues related to liquid freezing in the system, which can lead to damage and inefficiencies. By beginning with vapor from a vacuum level, the pressure is carefully controlled, allowing for a smoother transition to the liquid phase without the risk of freezing.
It's essential to manage the introduction of refrigerant carefully to avoid undesirable consequences. Starting with vapor ensures a controlled and gradual increase in pressure, minimizing the chances of freezing and safeguarding the integrity and efficiency of the refrigeration system.