What is the likely cause if an engine room exhaust blower runs but no air is exhausted?

When an engine room exhaust blower runs but fails to exhaust air, one likely cause is that the air inlet is under water. If the inlet is submerged, the blower will not be able to draw in air, leading to a situation where the motor operates, but there is no airflow being produced.

This scenario could occur in boats or vessels where the design might place air inlets low or near the waterline. As the vessel takes on water or during specific maneuvers, the inlet can become blocked by water, completely preventing air from being drawn into the blower, resulting in no exhaust air.

In contrast, other options such as a disconnected hose or a split hose would typically cause a lack of airflow due to physical blockage or leakage, but you would likely hear the blower struggling or detecting a difference in operation. Undersized wiring might affect the blower’s performance to some degree but would not directly cause the blower to malfunction in such a manner that it runs without moving air. Therefore, the condition of the air inlet is the most relevant concern when evaluating why the blower is not exhausting air as expected.