The VTech VacuTester is capable of detecting very small leaks, in the range of 1 x 10-7 mbar l/s, equivalent to 0.03 oz. of refrigerant per year, in coils, components or refrigeration systems. It is particularly suitable for high productivity operations.  
It involves pulling a deep vacuum in the chamber containing the unit under test (UUT) and injecting high pressure helium into it. Any resulting helium leakage is detected by the integrated mass spectrometer. The test result is Pass/Fail. In order to locate the leaking point, a manual sniffer leak detector must be used.