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Blower Motor Final Stage Unit Replacing
 
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Pelican Technical Article:

Blower Motor Final Stage Unit Replacing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$200

Talent:

****

Tools:

Phillips head screwdriver, T20 Torx driver

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Blower motor final stage unit

Hot Tip:

Use a T20 Torx socket for the rear fasteners

Performance Gain:

Proper working blower motor

Complementary Modification:

Replace cabin air filter

The blower motor controls airflow into the passenger cabin in conjunction with the blower motor resistor (final stage). It is mounted in the heater housing behind the right side of the dashboard. The blower motor speed is adjusted via the HVAC control panel through the blower motor final stage. The HVAC control panel receives a request from the driver/passenger, then sends a serial data signal to the blower motor final stage unit to the blower motor.

The blower motor final stage unit (resistor) is utilized to control blower motor speed. It receives the driver demand signal from the HVAC control panel and sends a high current signal to control blower motor speed. The blower final stage unit can fail resulting in a malfunctioning or inoperative blower motor. If you suspect your final stage is failing, look for the following symptoms: Blower motor speed fluctuates from high to low. Blower motor does not turn ON. Blower motor only runs at one speed.

Over time, a blower motor may become noisy as the motor electrical contacts wear. I have also seen debris from a rodent get trapped in the blower cage creating a vibration or noise. If your blower is noisy, pull it down and see if there is something stuck in it. If you find debris, be sure to clean out the HAVC housing before installing the new blower motor. The final stage unit does generally not cause vibrations. If you have a vibration, see our tech article on blower motor replacing.

If you're not sure which part is faulty, see our tech article on blower motor and final stage unit testing.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Working below the glove box, remove two T20 Torx lower trim panel fasteners (red arrows).
Figure 1

Working below the glove box, remove two T20 Torx lower trim panel fasteners (red arrows). The fasteners shown are Phillips head screws, however they should be T20 Torx, and someone has replaced them with the incorrect fastener.

Detach the lower corner of the lower trim piece (red arrow) by pulling down until the retaining lug disengages.
Figure 2

Detach the lower corner of the lower trim piece (red arrow) by pulling down until the retaining lug disengages. Pull the lower trim panel down from the dashboard far enough to access the footwell light electrical connector (yellow arrows). Disconnect the footwell light electrical connector by squeezing the release tab and pulling it straight out of the light. Then remove the trim panel from the vehicle. Be sure to store it in a safe place. 

Next, the lower blower motor cover (red arrow) has to be removed.
Figure 3

Next, the lower blower motor cover (red arrow) has to be removed.

Start by pulling the wiring harness out of the retaining tabs (red arrow).
Figure 4

Start by pulling the wiring harness out of the retaining tabs (red arrow). Then disconnect the electrical connection by squeezing the release tab and pulling it straight out of the blower motor (inset).

Working at the blower motor cover, remove the four T20 Torx fasteners (red arrows).
Figure 5

Working at the blower motor cover, remove the four T20 Torx fasteners (red arrows).

Remove the blower motor cover from the blower and store it in a safe place.
Figure 6

Remove the blower motor cover from the blower and store it in a safe place.

Working at the blower motor resistor (red arrow), disconnect the electrical connector by squeezing the release tabs (yellow arrows) and pulling the connector straight out of the blower motor.
Figure 7

Working at the blower motor resistor (red arrow), disconnect the electrical connector by squeezing the release tabs (yellow arrows) and pulling the connector straight out of the blower motor.

Next, remove the two T20 Torx fasteners (red arrows) from the resistor.
Figure 8

Next, remove the two T20 Torx fasteners (red arrows) from the resistor. Support the resistor as you remove the fasteners. Damage to the blower motor can occur if you do not.

Remove the blower motor resistor from the blower motor.
Figure 9

Remove the blower motor resistor from the blower motor.

Inspect the wiring harness that runs to the blower motor (red arrow).
Figure 10

Inspect the wiring harness that runs to the blower motor (red arrow). If there are signs of overheating or burning, replace the blower motor. See our tech article on blower motor replacing. Install the blower motor resistor in the reverse order of removing. Be sure that the electrical connectors are properly engaged. Listen for an audible click.


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Page last updated: Mon 12/5/2016 02:43:28 AM