Electronics cooling assembly with multi-position, airflow-blocking mechanism

A cooled electronics assembly comprising:

• at least one heat-generating electronic component;
• an electronics cooling assembly, the electronics cooling assembly comprising:
• an air-cooled heat sink coupled to the at least one heat-generating electronic component, the air-cooled heat sink dissipating heat from the at least one heat-generating electronic component to a cooling airflow passing across the air-cooled heat sink;
• an auxiliary air-moving device associated with the air-cooled heat sink and providing, when active, an increased flow rate of the cooling airflow across the air-cooled heat sink;
• and
• an airflow-blocking mechanism, the airflow-blocking mechanism toggling between a passive airflow position and an active airflow position, wherein in the passive airflow position, the airflow-blocking mechanism allows the cooling airflow to exhaust from the air-cooled heat sink without passing through the auxiliary air-moving device, and in the active airflow position, the airflow-blocking mechanism allows the cooling airflow to exhaust from the auxiliary air-moving device.