This 2003 Chevrolet Suburban came in with the complaint that the blower had lost speeds number 2 and 4. The customer was very concerned that the other speeds would soon fail too. This Chevy Suburban has manual HVAC controls so it uses a blower resistor assembly. 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. I do not recommend disconnecting the battery while this work is being done. Disconnecting the battery during the repair and then reconnecting it, will start the recalibration of the HVAC actuators. On older trucks you do not want to do this, unless absolutely necessary.
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, main ground and the third from the left, speed number 4. The burnt wire terminal on the purple wire is most likely why speed number 4 was not working. The heat damage to the black wire terminal meant that this Chevy was fixing to lose all blower speeds.
I have done a video on this this repair on a similar vehicle,as well. Please click here to view.