I am shy about recovering refrigerant from a system into a recovery cylinder (which is swapped with the parts house for reclamation with any type or condition of refrigerant throughout its life/use), performing a repair, such as a compressor or evap changeout, then reintroducing the recovered refrigerant back into the system.

In many instances, I may not be sure of the integrity of the original refrigerant charge (in the case of a first visit for instance), and certainly cannot be certain of the clenaliness of the bottle which I had contained the refrigerant into (oils, acids, what-not), and how certain can I be, through the process of operating the recovery machinery of no introduction of air, moist or not, into the container?

In the case of say an ice machine with up to 15# refrigerant charge, I particularly like to get off to a fresh start with some spankin' new gas.