Air-Conditioning Components and Systems Leak Tightness is defined by numerous specifications/standards in terms of g/yr of refrigerant loss. Implementation of these standards to a production leak tightness specification has been based on theoretical models that have resulted in potentially biased specifications that do not consider all micro-fluidic phenomena that can cause a given micro leak-path to be self-plugged. A generic method for leak tightness specifications known as Equivalent Micro-Geometry (EMG) is presented. The EMG is the maximum size of a micro-channel or pin-hole that will likely self plug during normal operation and therefore meets current environmental and functional specifications. The test method and apparatus used to empirically develop the proper EMG sizes and a correlation to refrigerant leakage is described along with examples of test results and recommended implementation steps.