Came out today for a Trane system not cooling. Upon inspection I found that the system was very low on refrigerant. I began to check all the connections for leaks. There was a small pin hole leak. I isolated the refrigerant into the condenser then closed both service valves. I recovered any left over refrigerant that was in the line set. I brazed the pin hole leak and pressure tested. The system held the pressure so I continued pulling a vacuum and recharging the system. I had to add 4lbs of 410-a refrigerant.