WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Vacuum - Cleaning Evaporator
Courtesy of VOLVO CARS OF NORTH AMERICA.
Clean the evaporator as much as possible with vacuum-cleaner through the hole in the evaporator housing for the power unit/fan resistor.