Blower motor
There are two parts that might need replacing in the blower motor: the control module and the brushes.
You might suspect the control module when the blower doesn't want to run at all (although there might be other reasons for this as well). Brushes are likely to be worn if the motor doesn't start one day but runs fine on the other. In this case, a moderate whack on the motor from below starts it nicely.
