Before using a recovery unit to remove a charge what steps should be taken

there are 4 steps that should be taken before using a recovery unit to remove a charge

Explanation:

A. The refrigerant should be tested for acid.

B. The recovery unit should be purged with nitrogen.

C. The recovery unit oil should be changed and recovery cylinder evacuated.

D. Service valve positions and recovery oil level should be checked, when applicable

y

Explanation:y