This 2002 GMC Sierra came in with the complaint that the blower would work sometimes, but now, it would not work at all. This truck has manual HVAC controls so it uses a blower resistor assembly. I do not recommend disconnecting the battery while this work is being done. Instead make sure the ignition remains off and remove the BLWR fuse from the underhood fuse box. This will ensure that there is no power on any wires while the work is being performed and it will prevent an unwanted recalibration of the HVAC actuators.
I recently completed a video of this repair on a similar vehicle. Please click here to view.
The blower resistor is located on the passenger side of the vehicle behind the glove box. There may be a plastic cover or hush panel that has to be removed to gain access to the resistor and wiring. Normally only the far right and center screws need to be removed to drop the panel down enough to work.
After the cover is removed disconnect the harness connector and inspect for damage. On this particular vehicle the only terminals that were damaged were the third from the right and the third from the left. Sometimes all of the terminals will be damaged and the plug will be melted to the resistor as shown in later in this repair.
In the pictures below you will notice that the black wire has substantial heat damage. The black wire is the ground for the blower motor and the high blower relay that is within the blower resistor assembly. When this circuit is lost the blower motor will not function at all.
For more testing information, please see the repair post at this link.