2004 Mercedes-Benz SL55 AMG Blower Motor Replacement Cost

When you turn on the heater, the blower motor blows it across the hot heater core, sending heat through the vents. Likewise, when the air conditioner is active, the blower motor blows air across the cold evaporator, which blows cold air through the vents.

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.

Driving with a defective blower motor means you won't have climate control — no air conditioning and no heat. It won't be comfortable — especially if you live in a place with extreme summers or winters — but it is unlikely to affect other components of the car or cause any damage.

There's no set lifespan for blower motors, but they tend to fail more often in high-mileage vehicles. Age can be a factor as the plastic fan blades become brittle over time. The amount of use a blower motor receives may also be a factor. Also, debris entering the HVAC box can destroy a blower motor regardless of mileage or age.

If the blower motor is making a grinding or rattling noise, it will be removed first for inspection. If it's defective, it will be replaced. If the blower motor isn't blowing air, the technician will first find and inspect any related fuses. If that's not the issue, the blower motor’s electrical connector is inspected to determine if power is reaching the motor. If that's not the problem, the blower motor will be removed and tested with an external power source. If the blower motor fails to operate under direct power, it will be replaced.

If the blower motor must be replaced, either the glove box or lower cover will be removed from the dashboard. This will provide access to the HVAC duct box, and the blower motor service cover. The service cover is removed, and the blower motor is disconnected electronically. Finally, the retaining screws will be removed, followed by the blower motor. The blower motor resistor will be installed into the new motor, and then they will be installed using the reverse of the procedure above.

If the blower motor is making noise, you should still be able to use the air conditioner. The motor will eventually fail once the noise has started, but until the vehicle is repaired or the blower motor fails, further use shouldn't cause new problems. The blower motor resistor can cause similar symptoms, but the fan would more than likely work on one or more settings until the resistor fails. When all fan speeds are not functioning, the blower motor is the likely culprit.

This procedure is best left to an fairly advanced DIYer or a professional. A basic understanding of a series electrical circuit, a few basic tools and a digital voltage meter are required. But diagnosis can be tricky, and there's significant labor involved in terms of removing the dash.