What causes the fan not to blow for the heat/ac?

Could be almost anything, fuse-- wiring circuit--faulty component. anything electrical, I check voltage and ground. At the blower motor wiring connector, two wires, the purple wire is voltage, the black wire is ground. You could take connector loose, use both ends of test light between those two wire terminals, key on, blower controls on. if the lamp comes on, I might suspect the blower motor itself? I don't want you to replace any component, needlessly, so you need to do some testing. You could use jumper wires from battery to blower motor, just to see if motor will run?