The energy demand of the commercial building sector is largely for cooling and heating and will eventually result in energy and environmental crises; therefore, enhancing the performance of the cooling and heating systems used in buildings is paramount. In response to this need, focus was set on the gas engine driven heat pump-combined system (GHPC)-consisting of a gas engine, single-stage vapour compression system, and single-effect absorption system that saves more energy as compared to a conventional gas engine-driven heat pump. However, so far, only the performance and transient characteristics of a fabricated GHPC have been investigated. Therefore, to ascertain the characteristics of the GHPC start-up dynamics under unsteady state operations so as to achieve efficient and stable start-up operation, experiments and simulations were attempted in this study. The transient behaviour from the start-up of this combined system in cooling and heating operating modes was also scrutinized. Accordingly, it was found that simulation results agreed well with experimental data. It was concluded that there were no large delayed responses in the absorption system during start-up operation when start-up of the absorption system is considered based on the system cooling capacity response after the solution pump starts. (C) 2017 Elsevier B.V. All rights reserved.