When the
blower motor fails, the air conditioner and heater may still work, and heat or cool may be felt at the vents, but the air pressure will be dramatically decreased. This will occur at all fan speeds, and all temperatures.
Another possible symptom of failure is a
rattling or grinding noise that comes from the passenger floorboard anytime the heater or A/C is active. This can be caused by broken fan blades, or a faulty bearing. This noise may come and go at random, and the fan speed may or may not change the noise.