After only one season a fan may be covered in enough gunk to give the illusion that the 'motor' is worn out, when really all that is needed is a good cleaning to keep it running for a lot more hours. I have often picked these up on trash day, and gotten years of use from them. Rarely I may have to replace a knob, but usually they are functioning, but the blade speed is about half of normal.
Step 1: Tools
All Purpose Cleaner/degreaser
Finger Nail Brush
green kitchen scrubbies
Step 2: Remove front and back grills
Sometimes a few can be missing OR the hole has grown too large to reseat tightly.
Yes, you can skip a few, usually you can leave off a side screw without TOO much noise factor.
but you NEED the top and bottom tightly screwed down of the vibration will make a hell of a racket.
scout around for replacements - you want short and fat threads.
Step 3: Remove grill and fit
if the feet are missing you will have to dummy a replacement, or just make sure the fan is propped up, like in a window. Vibration at high speeds will make the fan walk and possibly fall.
Step 4: Brush the motor
Use a brush to remove the hair and gunk.
also wipe the struts.