1997 Nissan Sentra Heater Blower Motor

My daughters 1997 Sentra has a problem with the heater blower motor. THis blower has 4 levels of intensity and it only works on the highest setting of 4. THe fan does not operate on the lower three settings. I am assuming that the blower either works or it does not work, which means it is getting power.
Question is would it be the blower motor OR the switch on the dash that turns it on that needs to be addressed.


If it is the switch, how do you access this item. DO you have to drop the whole dash to get at it?

Please advise.

THank you