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What action should be taken prior to charging an R-11 system with liquid refrigerant?

  1. Reduce system pressure to 2 mm Hg

  2. Establish a vapor pressure of 16.9 inches Hg

  3. Check the power supply

  4. Flush the system with nitrogen

The correct answer is: Establish a vapor pressure of 16.9 inches Hg

Establishing a vapor pressure of 16.9 inches Hg is crucial before charging an R-11 system with liquid refrigerant because it ensures that the system is in the correct state to receive the refrigerant. This vapor pressure helps in accomplishing two main objectives: it indicates that the refrigerant is at an appropriate temperature for charging, which minimizes the risk of liquid slugging, and it ensures that any moisture or contaminants have been effectively removed from the system. Maintaining proper vapor pressure is also essential for the overall efficiency and function of the HVAC system. It allows the refrigerant to absorb heat effectively when it evaporates and provides an environment where the refrigerant can circulate properly. By ensuring that the system's vapor pressure is appropriately set, technicians can facilitate a safe and efficient charging process, leading to optimal performance and longevity of the system. In contrast, the other options do not specifically address the prerequisite state of the refrigerant system prior to charging. Reducing system pressure to 2 mm Hg may be relevant for certain system procedures but does not directly pertain to the vapor pressure needed for charging. Checking the power supply is also important in a general sense but is not a specific preparatory step for refrigerant charging. Flushing the system with nitrogen