WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Side Compartment, Panels, And Screws
Courtesy of VOLVO CARS OF NORTH AMERICA.
Remove:
panels (B) over seat rails.
4 securing screws (C) in seat rails.
connector to heater pad and control module (under seat).
Lift seat straight up (locating pins in front and rear edges).