When the front blower for heat and a/c work fine and the rear does not on the 2001 GMC Yukon it could be a blown fuse. Automobile manufacturers rarely have both of these blowers running off the same fuse.
where is blower motor resister located on 2001 GMC Yukon
If you are referring to the blower motor only working on the high speed setting, then the problem is the blower motor Resistor Pack is defective. Replace it. It can be the blower motor speed control switch but not likely.
Have you checked your liftgate fuse? In my 2006 Yukon, when the liftgate fuse went out the rear ac wouldn't work nor would the electric locks for the liftgate itself.
Passenger floorboard
There is no filter on a 2003 yukon, GM stopped inside filters in 2002
under right side of dash
under right side of dash near blower motor
The '97 GMC Yukon heater/A.C. blower motor is found under the glove box inside the truck. You can see it just by looking. No need to remove any panels etc! (A good "tap" will get it to work if it is just a loose connection) Kenny S.
I am assuming you are referring to the air conditioner blower motor. If so, check the fuses first. The resistor could be defective as well as the relay and fan motor.
Any of the following................... 1. Low coolant level. 2. Clogged heater core. 3. A/C heater controller bad. 4. A/C heater doors not working. 5. Vacuum problems........
That normally happens if one of your flasher bulbs is not working
Check the fuse marked "IPC".