Heater fan on 2002 Yukon does not operate in front, only rear.

The front blower motor is controlled by the blower resistor module.This is usually the problem with the front blower not working.I looked up the schecmatics and I don`t see separate fuses for the front and rear.But the fuse for the front blower is in the under hood fuse block.If this is good then The problem is probably the resistor module.It is next to the blower motor.The connector from the resistor connects to the blower motor.If you want to confirm this you can check for power and ground at the blower motor connector when you activating the blower switch on.This can be done with a test light.Make sure you have power going into the resistor module also.If you have power going in and no power at the blower motor then replace the resistor.Hope this helps.Good luck.