To add small amounts of refrigerant to the low side of an air conditioning system, the refrigerant should be introduced through a particular valve and in a particular state. What valve and state combination is correct?

Correct Answer: Option B — suction service valve as a vapor

Adding refrigerant to the low side while the compressor is operating requires introducing it strictly as a vapor through the suction service valve to protect the reciprocating compressor from hydraulic shock and mechanical failure.