From the primitive two-speed bladed fans of yesteryear, to the infinitely-variable computer-controlled blowers of modern luxury cars, automotive ventilation systems have helped provide for comfortable and safe vehicle operations for decades. The speed of the air flow through ventilation systems has vastly improved in recent years, due, at least in part, to better construction and configuration of blower motors and impellers. Certain system shortfalls may mimic some symptoms of blower motor failures, of one type or another, and accurate diagnosis depends on their recognition.
The blower motor may seem to be to blame when air flow becomes notably decreased, when if fact, the fault lies elsewhere. Insufficient flow at all blower speeds might be caused by a clogged air intake screen. Leaves, or other debris that obstruct the screen can make the blower motor efforts seem feeble, at best. Any debris particles that enter the plenum may contact the blower impeller, and the sounds produced could raise undue suspicions of motor infirmity. Faulty operations of doors in the ventilation plenum can misdirect air flow, and output at any vent register can be weakened. Discrepancies in the electric circuit for the blower, such as bad control switches or resistors, can halt all function, or prevent operation at certain speed settings. Once these possible causes are eliminated, remaining symptoms may indicate emerging blower motor failures.
A weak blower motor may not clear interior glass as well as before. Sudden or evolving needs for manual efforts to dry the windshield might be an indication of reduced blower performance. Moisture collecting on interior trim, or exceptionally increased condensation output at the air conditioner drain, could also signify fading blower action. Frost that forms in the engine compartment, on air conditioner plumbing, may also indicate a lack of air flow in the plenum chamber. Smoke originating from the vent registers, or from under the dash, can be signs of catastrophic blower motor breakdowns.
Unusual sounds emanating from the dashboard might be the first tell-tale signs of trouble with a blower motor. Squeals or squeaks that begin with blower operation, but fade to silence soon after, might be the only signal granted of motor bearing problems. The bearings are seldom serviceable, and the remedy requires motor replacement. This symptom is best acted upon quickly, to avoid imminent and complete loss of air flow. Clicking noises that rhythmically coincide with blower speeds may signify some discrepancy of the blower impeller, if debris in the area has ruled out as the cause. The plastic impeller can suffer breaks from the introduction of foreign objects, like coins, or fatigue due to radical temperature changes normally experienced in a vehicle ventilation system.
Vibrations felt in the dashboard, or neighboring interior pieces, that increase with blower speeds are possible signs of an out-of-balance condition in the motor, or impeller. The constant vibrations may not affect air flow to any substantial degree, but the motor is incapable of surviving such hardships for long. Slight wisps of smoke might be confused with mists produced in humid vehicles at first sight, but the smell of electrical component failure quickly corrects any misgivings. Odors that are amplified by raised blower speeds might result from lackluster blower performance over an extended time period. Inappropriate ventilation selections, or heavy smoking in the vehicle can also be to blame. Cleaning the blower impeller and ventilation plenum may restore full function, in this instance.
