Off-design Performance of a Louvered Fin-Tube Heater Core in an Automotive Climate Control System

•A commercial ACCS results in unique flow features interacting with the heater core.•Previous studies have not accurately modelled or replicated the unique flow features.•Thermal performance of a heater core in an ACCS is up to 60% lower than expected.•Several off-design features act in combination to deteriorate thermal performance.•Only 50% of the deterioration in performance could accounted for.