The primary objective of this study was to optimize the production line of chillers equipped with free-cooling capability and multi-fan condenser systems, with a focus on enhancing operational efficiency and final product quality at a manufacturing plant located in northeastern Mexico. A quantitative approach was adopted using a pre- and post-intervention experimental design within the Six Sigma framework, following the sequential DMAIC methodology. The sample comprised operational and quality data collected directly from the production line at critical control points, where out-of-tolerance dimensional deviations and electrical continuity issues were identified. Data collection and analysis instruments included SIPOC and QFD diagrams, check sheets, Pareto charts, control charts, process capability studies, as well as cause-and-effect matrices and process-level FMEA for risk quantification. The results revealed that the primary sources of defects were associated with inconsistencies in harness design, insufficient dimensional control during material receiving, and the lack of standardized assembly procedures. Following the implementation of corrective actions, such as comprehensive drawing reviews, supplier standardization, process reconfiguration, and cross-training of personnel, rework was eliminated, cycle time was reduced by more than 20%, and costs related to additional materials were significantly decreased. Financial analysis confirmed a positive net present value (NPV) and a substantial reduction in monthly operating costs. In conclusion, the disciplined application of the Six Sigma DMAIC methodology, supported by statistical tools, enabled sustainable improvements in complex manufacturing processes, strengthened the culture of continuous improvement, optimized resource utilization, and enhanced competitiveness within the industrial heating, ventilation, and air conditioning (HVAC) sector.