What occurs when the defog switch is activated?

When the defog switch is activated, the defog valve opens. This is crucial for managing cabin conditions, particularly in aircraft or vehicles where visibility can be affected by fog or condensation on windows.

The defog valve allows warm, dry air to flow onto the windscreen or windows, effectively reducing moisture and improving visibility for the operator. This is essential for safe operation, as clarity is vital in various environments.

While other choices mention the state of valves or air conditioning, only the opening of the defog valve directly relates to the function of defogging the windows by promoting airflow that helps to clear moisture, ensuring optimal visibility.