When Cleaning Defroster

WARNING: This page is about a different car, the 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Setting Controls To Defroster

Courtesy of VOLVO CARS OF NORTH AMERICA.

Set the controls to "defroster" and run the blower fan at its highest speed.
At the same time vacuum the windshield and side window defroster vents using a vacuum cleaner.
Clean and vacuum with windshield removed if removing windshield.