Mobile air-conditioning (MAC) systems represent a significant source of energy consumption in passenger vehicles, particularly under real-world operating conditions. Improving the efficiency of these systems is crucial for enhancing overall energy performance while ensuring occupant comfort. Efficient MAC systems may qualify as eco-innovative technologies under Regulation (EU) 2019/631, effective from 2025. This study establishes a methodology for quantifying CO₂ savings associated with eco-innovative MAC systems in passenger vehicles. The approach compares CO₂ emissions from baseline and eco-innovative vehicles with both active and inactive MAC systems. Ambient conditions derived from existing literature are applied to represent typical European MAC usage scenarios. The testing protocol follows the WLTP procedure under controlled environmental conditions, including temperature, humidity, and solar radiation, with the possibility of simulating or omitting certain conditions through equivalent testing options. Vehicles are categorized into MAC Test Groups based on consistent characteristics such as powertrain type, MAC compressor design, and body configuration, facilitating a streamlined testing process. Preconditioning and soak requirements are defined to ensure testing consistency. CO₂ savings are determined by calculating the difference in tailpipe emissions with and without MAC activation for both baseline and eco-innovative vehicles. The methodology is designed to accommodate various powertrain configurations, from conventional to electrified vehicles, through an internally developed vehicle model that estimates baseline vehicle CO₂ emissions.