This Standard is restricted to refrigeration circuits that provide air-conditioning for the passenger compartments of passenger and commercial vehicles. This Standard includes analytical and physical test procedures to evaluate refrigerant concentration inside the passenger compartment. In the early phases of vehicle evaluation, usage of the analytical approach may be sufficient without performing physical tests. The physical test procedure involves releasing refrigerant from an external source to a location adjacent to the evaporator core (inside the HVAC module). An apparatus is used to provide a repeatable, calibrated leak rate. If the system has multiple evaporators, leakage could be simulated at any of the evaporator locations. This standard gives detail information on the techniques for measuring R-744 (CO₂) and R-1234yf (HFO-1234yf), but the general techniques described here can be used for other refrigerants as well.