Hello I have an 02 gmc and when I turn on the heat or the air I get nothing. I don't even hear the blower kick on. Before I lost all functions It use to blow out ice cold air just no heat. Any thoughts? I'm hoping I don't have to replace the whole hvac system.

If you do not hear the fan blower running at all and you have checked the fuse it is probably the blower fan resistor normally it is located under dash passenger side,attached to blower housing, check connection first for corrossion or burnt wires and replace.

The blower resistor is the most common thing to fail on these. Mounted under the dash on the passenger side, behind the blower. As far as no heat, It could be the heater core, the blend door motor, or the controller. My guess on that would be the blend door motor. It is located in the middle of the dash, just under the radio. If you have a center console, you may be able to get to it from the side.