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Blower Motor Testing
 
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Pelican Technical Article:

Blower Motor Testing

Nick Czerula

Time:

3 hours3 hrs

Tab:

$200

Talent:

****

Tools:

Phillips screwdriver, DVOM, fused jumper test leads

Applicable Models:

Z4 M54 (2003-05)
Z4M S54 (2006-06)
Z4 N52 (2006-06)
M3 (N/A-A)

Parts Required:

Blower motor

Hot Tip:

Be careful not to damage blower housing

Performance Gain:

Replace faulty blower motor

Complementary Modification:

Replace blower motor and final stage together

BMW Z4 vehicles can come equipped with one of two climate control systems. IHKS manually controlled climate control, or IHKA, automatic climate control. Each has multiple sensors, controls, air temperature units and ducts. IHKA has additional components to handle auto temp control. The blower motor which controls air flow into the passenger cabin, is among the most consequential components in the climate control system. The blower motor resistor (or final stage) varies voltage to the blower motor to achieve the desired speed. The blower motor is a D/C electric motor driven by varying current supplied by the blower motor final stage unit.

If your blower motor fails, replace the blower and resistor together. You don't want to have to go back in if one fails later. Over time, a blower motor may become noisy as the motor electrical contacts wear. The blower fan cages also fracture, creating a vibration when the blower is ON. If it fails or becomes noisy, you can use this procedure for the repairs.

Testing the blower motor is no easy task. You will have to work high up behind the instrument panel in an uncomfortable position.

Usually when the blower motor resistor fails, the blower motor will work in only one speed, or fluctuate when a set speed is selected. Most times it defaults to high speed, leaving other speeds not functioning. To confirm the resistor is the root problem on your X3, test it first.

If you try to change the blower motor speed and nothing happens you may have a blown fuse, a bad blower motor or a bad blower motor resistor. There have been cases where the final stage has kept the blower motor running while the ignition key is off, therefore draining the battery and leading to a "no-start" problem the next morning. In this tech article we are going to review how to test each component in the system

While in there, replace the cabin microfilter. It needs every other oil change anyway and the dirt restricts flow and reduces heating and cooling efficiency.

Remember your car may have been serviced before and 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 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. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Remove the glove box and right side knee airbag. See the tech articles for the corresponding procedures.

Once the right knee airbag is removed, you have a clear view of the blower and final stage.
Figure 1

Once the right knee airbag is removed, you have a clear view of the blower and final stage. More instrument panel parts have to be removed to get them out, but you can test them at this point. When testing, you will have to reconnect the battery, which will set an airbag fault code when the airbag is removed. Keep this in mind, as this fault code will have to be cleared using an advanced BMW scan tool. The blower final stage is located to the left (red arrow) of the blower motor (blue arrow).

Before testing, confirm the wiring on your vehicle.
Figure 2

Before testing, confirm the wiring on your vehicle. I always test at the resistor. Check with the latest repair information. On my subject vehicle, 2006 Z4M, the wiring was the follow; red arrow blower speed control from IKHS(A) (battery volts varies with speed), blue arrow ground (zero volts), purple arrows voltage output to blower motor (varies depending on blower speed), yellow arrow battery volts all the time from fuse 30 (40 amp) in the power distribution panel.

Disconnect the blower motor electrical connector by pressing the release tabs (red arrow) and pulling it straight out.
Figure 3

Disconnect the blower motor electrical connector by pressing the release tabs (red arrow) and pulling it straight out.

Turn the key ON and set the blower speed to HIGH (green arrow).
Figure 4

Turn the key ON and set the blower speed to HIGH (green arrow). Start by connecting your DVOM across blower motor output connector. Connect your red lead to terminal 2, on my vehicle this is red and blue (yellow arrow). Connect your black lead to terminal 1, on my vehicle this is the black and green wire (purple arrow). The blower speed should be set to high. Your DVOM should read battery volts (red arrow). If the blower motor is running, it will be about 12 volts with a vehicle power supply on. If just testing using your battery, expect a 2 volt drop from what open circuit battery voltage is at the time. If you get no voltage, try cycling the key off and waiting one minute, then cycling the key on with your DVOM already in place. If you have zero volts or lower than battery volts, the final stage unit may be faulty. If you have voltage but no blower motor operation, the blower motor is likely faulty. Keep in mind the blower resistor supplies ground to the motor. Earlier we checked the fuse and confirmed it to be good. You can also move the black lead of your DVOM to battery negative (ground) and keep the red lead on terminal 1, you should have battery volts. If you don't, there may be an open circuit between the fuse and the connector. Test note, 100% speed will be about battery volts, 50% speed will be about 8 volts.

To test the IHKA(S) output to the resistor (control circuit), connect your DVOM black lead the ground and the red lead to the red and green wire at the blower final stage (blower speed control from IKHS(A) (battery volts varies with speed).
Figure 5

To test the IHKA(S) output to the resistor (control circuit), connect your DVOM black lead the ground and the red lead to the red and green wire at the blower final stage (blower speed control from IKHS(A) (battery volts varies with speed). Rotate speed knob to one click from off (purple arrow), DVOM should display about 1.8 volts, then rotate knob to 50% (red arrow), DVOM should display about 4.8 volts, then rotate knob to high (yellow arrow), DVOM should display 8.25 volts. If this voltage is missing or incorrect, the issue may be with the IHKA(S) control. Check fuse for the control head and run a test using a BMW scan tool to be sure. If you have this voltage but no output to the blower, the final stage unit is faulty.

To check if the issue is the control head, you can activate the blower using a scan tool as well.
Figure 6

To check if the issue is the control head, you can activate the blower using a scan tool as well. Once activated, use the steps above to check for voltage to the blower and control voltage to the final stage unit. Test note, 100% speed will be about battery volts, 50% speed will be about 8 volts.

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Page last updated: Fri 12/9/2016 03:06:40 AM