The specialized book "On-site diagnostics of the mechanical ventilation and cooling sources" offers a comprehensive analysis of mechanical ventilation and cooling systems in two office buildings. The authors, Monika Blaszczok and Malgorzata Król, present the results of their research, which is based on the inspections and measurements conducted. A central aspect of the investigation is the comparison of the results with the existing design documentation. The authors address the discrepancies between the documentation and the actual installation status of the systems in both buildings. Additionally, the challenges encountered during the measurements are discussed in detail. This book is aimed at professionals and students in the fields of mathematics and natural sciences who are engaged in the diagnostics of technical systems.