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 Voltage Display
Courtesy of VOLVO CARS OF NORTH AMERICA.
The relay controlling the low speed fan is faulty or the relay is always engaged, even with the ignition in position 0 (check that there is not 12 V at the red/blue cable terminal 2 at the relay).