After recovering refrigerant from a sealed system if nitrogen is used to pressurize or blow debris out of the system the nitrogen:

After recovering refrigerant from a sealed system, if Nitrogen is used to pressurize or blow debris out of the system, the nitrogen can be vented because air is composed of 80% of Nitrogen gas. 

After recovering, the refrigerant should be returned to the appliance from which it was removed.

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because growing process had stoped after 4-5 year