As a licensed and fully qualified residential HVAC repair contractor in the Minneapolis–St. Paul Metro Area, we strongly advise that you DO NOT attempt this job. Today’s central air conditioning and heat pump systems and ductless mini–split AC systems require exactly the right amount of refrigerant to operate properly. It’s not a job for amateurs. Instead, call us if you suspect you need to add refrigerant to your system. We’ll make the proper tests, identify the reason for low refrigerant levels, and make any needed repairs. Then, we’ll add exactly the right amount of refrigerant. Don’t risk damaging your equipment.