We have a coleman mobile home furnace that will com on heat no problem however the blower screeches like metal grinding on metal the blower turns but the screeching is deafening. We don know how to fix it. We've taken it apart but can see what's wrong with it.

Screeching is usually associated with the blower cage hitting the box in which it is mounted. Look for loose screws holding the motor in, a broken mount or a loose screw holding the cage to the motor shaft. Could be a bad bearing in the motor too.