In an energy harvesting sensor actor network, a node recharges its battery from harvestable sources, such as solar, wind and vibrations. Sustainability of the network till next recharge time is one of the most important challenges in harvesting sensor networks. In this paper, a fuzzy based adaptive duty cycling algorithm has been proposed to achieve the network sustainability in harvesting sensor actor networks. In this work, current residual energy, predicted harvesting energy (for a futuristic time slot) and predicted residual energy parameters are considered as fuzzy input variables to estimate duty cycle for a sensor node. In this work, a harvesting model has been adopted to predict the harvesting energy. Further, residual energy has been estimated for future time slot using predicted harvesting energy, energy consumption model and current residual energy. Simulation results are presented to show the efficacy of the proposed mechanism by considering network sustainability metrics, such as number of rounds in which network is connected, the round at which first node dies, maximum number of dead nodes and average number of received packets at the actor node.