Answer:
B. Immediately close the valve in the service line and charge the system
Step-by-step explanation:
The precaution should be taken prior to recovering refrigerant from a chiller are:
1) Immediately disconnect the recycling or recovery equipment and open the system for service.
2) Wait for at least a few minutes to see if the system pressure rises, indicating that there is still refrigerant in liquid form or in the oil.
3) Immediately break the vacuum with nitrogen and open the system for service.