I have a 1995 1/2 ton 2WD Chevy pickup. The heater fan motor has been giving me fits for a while now. I have replace the resister that is behind the glove compartment, the switch that is on the dash and pulled the motor out and attached it to the battery to make sure that it worked. What is the problem?

Check the fuse and blower motor relay in the under hood fuse/relay box.

I hope you don't have this issue. I had a car, that whenever the weather got cold the blower motor would "fall" and start to scrape. I could push it back up. Of course it eventually would not work. Took out the brushes and the blower resistor. There was a service bulliten, but I had to devise my own fix. I discovered the problem too late. Fix cost a few dollars in parts using brushes from a vacuum cleaner store.