Presently, auto manufacturers do not have do not have efficient or accurate methods to determine the amount of refrigerant (R-134a) in an air conditioning system of an automobile. In the research presented, vibration analysis is examined as a possible method to determine this R-134a amount. Initial laboratory tests were completed and experimental modal analysis methods were investigated. This approach is based on the hypothesis that the natural frequency of the accumulator bottle is a function of the mass of refrigerant in the system. Applying this theory to a working automotive air conditioning bench test rig involved using the roving hammer method—forcing the structure with an impact hammer at many different points and measuring the resulting acceleration at one point on the structure. The measurements focused on finding the natural frequency at the accumulator bottle of the air condition system with running and non-running compressor scenarios. The experimental frequency response function (FRF) results indicate distinct trends in the change of measured cylindrical natural frequencies as a function of refrigerant level. Using the proposed modal analysis method, the R-134a measurement accuracy is estimated at ±3 oz of refrigerant in the running laboratory system and an accuracy of ±1 oz in the non-running laboratory system. / Master of Science