My heater/blower had cut down to half power then it eventually stopped working altogether, i looked on this forum and another Volvo forum and bothe said it was either the common resister for the blower or the motor, so i decided to change mine but could not find a walk through for an S60 so decided to make one when i was changing mine!
open glove box pull open and on top right there is a strut as below
pull strut towards you and it will pop out, then open glove box full as below, pull hard and the plastic clips will slip through catch without breaking allowing the glovebox to open fully
unplug grey plug for glove box light (at back)
undo screws under dash next to footwell courtesy light
and remove covering panel as below to gain access to blower motor and cabin filter
undo all screws holding glove box to dash, (2 on top 3 down each side)
unplug footwell courtesy light (green plug ) this will allow you to remove whole glove box completly
pull up side paneling holding carpet down (held on with plugs come away easy try not to twist or you might snap plugs)
pull back carpet, blower is located on left under dash as per picture
pull out large grey plug from blower motor (for referance white box with black lid on right in picture is cabin/ pollen filter 4 screws to access)
undo brass coloured screws (all star T25 multipoint) holding blower in place and pull out hoses attached to it (remember where they go back and what position the whole unit goes back into place) screw at back requires flexi adjuster or screw driver as shape of bulk head affects ability to access with straight socket/ driver
pull out old blower may take some fettling but it will come out with a little determination and alot of swearing
reverse whole process fitting new motor
hope yous find this usefull