单选题When adding oil to a refrigeration system, precautions must be taken to ensure that （）.Athe compressor suction pressure is not too highBall air is purged from the pump and charging fittingsCthe high pressure cutout switch is held open to prevent accidental startingDthe condenser is completely shutdown first
单选题
When adding oil to a refrigeration system, precautions must be taken to ensure that （）.
A
the compressor suction pressure is not too high
B
all air is purged from the pump and charging fittings
C
the high pressure cutout switch is held open to prevent accidental starting
D
the condenser is completely shutdown first
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