Rapid growth in energy consumption is one of the major challenges for the development of the data center industry. Cooling equipment accounts for roughly 40% of energy consumption in a typical data center. Free air cooling (FAC) is a method for substantial energy savings in cooling, and it is increasingly being implemented in data centers. However, this cooling approach may cause reliability risks for the telecom equipment due to the increased temperature range and often the removal of the humidity control in FAC implementation. This paper overviews the potential reliability risks from FAC, and then presents a prognostics and health management (PHM) to evaluate and mitigate these risks. This prognostics-based approach can provide early warnings of failures to schedule maintenance and thus reduce unscheduled data center downtime. This approach also enables FAC implementation in existing data centers that were not initially designed with this cooling regime.