Hyundai Repair: blower motor, blower motor, sonata

Question
I have a 2002 Sonata

The blower motor is not working properly:

Sometimes it doesn't blow at all.

Other times you can hear it running, but no air is coming out of the vents

Most of the time it operates normally.

Any suggestions?  

Answer
I'm a little curious about hearing the blower running but no air coming out of the vents.  If you hear the blower running, air should be exiting somewhere: the dash, floor, or defrost vents.  Does the blower sound normal when no air exits?  If not, try to describe the noise for me.

The other symptoms you describe suggest an open circuit in the blower switch or a worn blower motor.