The front of a rack-mounted 2 RU (Rack Unit) chassis includes bays that receive replaceable components, such as storage drives. Two rear slots of such chassis each receive hot-swappable 1 RU servers that couple to a midplane of the chassis. When a server is removed from its slot while the server in the other slot remains operational, the airflow output of the operational server escapes via the empty slot rather than cooling the components in the front-facing bays. Embodiments provide a single-blade air damper that blocks airflow via an empty chassis slot. The single-blade air damper is connected to spring assemblies on both chassis sidewalls. The spring assemblies are maintained in unstable states when servers are installed in both slots of the chassis. Upon a server being removed from a slot, the spring assemblies transition to stable states that position the single-blade air damper to block airflow via the empty slot.