Blower not working

Could be either one.
Start with the simple stuff first... check your fuses and relays.
The switch, you remove it, determine which input is for power, which is for ground, then you run a continuity test with a digital multimeter.
The blower motor... expose it and unplug it. You can take a test light or Power Probe and verify that you have power going to the blower motor... to verify that your ground is intact, you'd want to use something like a Power Probe or "logic tester" style of test light. If you don't have power, and your fuses and relays checked out, and your switch checked out, then it's a matter of tracing wires. If you do have power, then you supply power to the blower motor itself (because, even though you have power, you might have insufficient current at the intended source, still), and if it doesn't respond, you know your blower's bad.
As for how to access it on the Volvo, I'll leave that to someone in the know... I could tell you how if it was a KW, but I've never had to do this on a Volvo.

 

Blower is PWM controlled from Climat Unit. There is motor PWM driver, it is mounted on C-shaped radiator, speed is controlled with n-channes MOSFET, try to solder in new one

 

To get to the blower on a 2nd gen volvo remove the right dashboard panel. You'll need to remove the grab handle first and one of the dash panel mounting bolts is under the right hand speaker cover. Once the panel is off you'll be looking at a black plastic box for lack of a better word. Your fan is inside that box at the bottom. Remove a bunch of those little metal clips with a small prying tool being careful not to distort them because you'll reuse them to put it back together. Drop the bottom part off and the blower IIRC will slide out.

 

https://www.youtube.com/watch?v=v4SX-1DxhHw

Great video from OTR step by step walk through. Good luck!