Tested system not cooling for the upstairs. System was flat on refrigerant and conducted a nitrogen leak test. Found the system was holding 305 psi with no issues and ended up finding the Schrader valve leaking from the low side service valve. We replaced a Schrader valve, pulled a proper vacuum on the system, and filled the system up with 7 pounds of refrigerant. Tested fully after repairs made, and found no failures at this time.