A system for applying suction to a wound uses a reference airflow for monitoring system operation. A reference airflow (or "controlled leak") to the suction source is provided when the system is in operation, such that deviation from the reference airflow can be monitored as an indication of a change in operation, such as a leak in the seal of the wound cover, a blockage of airflow from crimping of the suction conduit or overfill of the waste collector, or an inadvertent turn off or disconnect from the suction source.