Simple thermodynamic and heat transfer mathematical models have been developed to aid in the study of HVAC system designs in field testing. The refrigeration system, heating system and vehicle cabin have been examined.Test data are used to determine parameter values in governing equations. These parameter values may be used for performance simulation and competitor comparison. A benefit of this approach is that individual component performance can be extracted from system performance. Another benefit is that performance data can be adjusted, for comparison purposes, to identical test conditions.