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

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

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