Why is it important to achieve a deep vacuum free of moisture before charging a refrigerant system?

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Moisture in a refrigerant system is dangerous because water can drive chemical and physical problems that harm performance and longevity. When water is present, it can react with refrigerant and oil to form acids, which attack metals, seals, and bearings and can create sludge that clogs passages. Water can also freeze in the low-temperature parts of the system, such as the metering device or evaporator, blocking flow and reducing cooling. All of this leads to lower efficiency and greater risk of component damage. A deep vacuum is used to remove moisture so, once the system is charged, water isn’t there to cause acid formation, ice blockages, or corrosion, preserving performance and reliability. Moisture doesn’t improve lubrication, and it's not harmless—nor is it related to engine corrosion.