Found system out of 410A refrigerant. Put 1lb 410A and filled to 450lbs with nitrogen and ran leak search. Found no obvious leak at first, so climbed back through attic and checked line set. Found no leak at line set in attic. After extensive search I found leak only after taking off my hoses and valve stem came out. Installed new valve stem on suction line service port. Tighten down everything and vacuumed system down below 400 microns and recharged system. vacuumed to 270 microns had rise of 76 in 15 minutes. System is now working within factory specifications.