Converted the refrigerant on a 115-ton Trane rooftop unit from R-22 to R-407c. System was flushed and compressor oil was replaced multiple times and tested with a refractometer to insure proper removal of mineral oil. Filter dryers, Schrader cores, and high pressure switches were replaced. Identified and repaired system leaks during the course of the work. Mechanical cooling downtime was limited to three days to minimize impact on facility.