The aisle capping has been attracting attention as a method for reducing power consumption of an air-conditioning (A/C) system in data centers and central offices. This method designs airflow pattern so as to confine supplied cold air to cold aisles, by encircling it with top panels and wall panels. This paper discusses optimization of operational conditions for an A/C operation with the aisle capping method, presenting experimental results conducted in consideration of a telecommunication service provider's central office environment. In the experiments, heat generation from network equipment was simulated using heat radiators. The A/C system's power was quantified and compared for various cooling conditions. Also, fault tolerance was investigated for the conditions. Through these discussions, we describe the favorable effects that the aisle capping could have.