When a system is in deep vacuum, what should you do?

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Deep vacuum means there’s little to no refrigerant in the system, and moisture and noncondensables may be present. Energizing the compressor under these conditions is dangerous because the compressor needs refrigerant flow to lubricate and cool properly. Without refrigerant, lubrication is compromised, the oil can’t circulate correctly, and any moisture inside can flash into steam, potentially causing corrosion, acid formation, or mechanical damage. The safe approach is to keep the system powered off and finish evacuating and then properly charging the system before starting it again. Opening the service port to atmosphere would reintroduce air and moisture and ruin the vacuum, and trying to push pressure in manually or using the compressor to “purge” moisture would also lead to unsafe, improper conditions.