How do you check the functionality of the heater and defroster?

The functionality of the heater and defroster is best checked by turning them on and assessing whether they operate effectively to clear the windshield. This method provides a direct observation of their performance during an actual operation that simulates real driving conditions. By assessing their effectiveness at clearing the windshield, you can determine if they are functioning properly and able to provide adequate visibility, which is crucial for safe driving.

While checking visual indicators on the dashboard may provide some information about the system's status, it does not guarantee that the heater and defroster are functioning effectively. Similarly, listening for unusual sounds during operation can help identify issues, but it does not measure their ability to clear the windshield. Finally, checking the temperature of the air flowing can give some indication of the system's performance but does not confirm that the defroster is effectively clearing any moisture or frost from the glass.

Therefore, directly testing the heater and defroster in action by ensuring they operate effectively to clear the windshield is the most comprehensive approach to verify their functionality.