Evacuation valves
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.
The evacuation valves are used to even out the pressure in the passenger compartment.
The rubber dampers in the evacuation valves open when the air pressure is slightly higher in the passenger compartment than outside. When the air pressure is the same on the inside and the outside, the rubber dampers close. This prevents water and air (odors, dust and exhausts fumes) from penetrating the passenger compartment.
NOTE:
The evacuation valves must not be blocked, this will impair the function of the climate control system.