Blower Motor Regulator Replacement
There are some good threads on Duo Valve problems that you should look search for on the DIY stickies.
More often than not, the blower motor is fine, and its the voltage regulator that goes bad. One way to diagnose this is to use you A/C pushbutton control module. Steps:
- Ignition on
- Press A/C auto to 72F
- Hold Rest button for 5 sec or until left side diplay says "1"
- You can now see actual sensor values for your car
- Pressing AUTO button on one side makes sensor positions up or down.
- Pressing the opposite side AUTO button makes the sensor position go in the opposite direction.
- Press the AUTO button until the left hand number is 10, this is blower control voltage. 6.0 corresponds to 6 volts, which is max voltage applied. If there is 6 volts applied to the regulator, and the blower is not going like crazy you probably have a bad regulator. If no voltage is present, then its an upstream electrical component. The normal failure of the regulators is a slow degradation, so your description does not match the usual fault.
Shown below are some excellent instructions on older vintage W210 voltage regulator replacements. When I used these instructions, my only exception was to crimp the connections, and then securely tape them together to avoid vibration induced failure. Its an easy replacement, 1.5 hrs with the right tools and mindset. Also, spending $150 beats spending $1,000 for motor blower and regulator replacement. Later vintage W210s do not require wire splicing, and its a plug in for the newer regulators. These steps can also be used to remove the blower motor/regulator unit so you can do a little troubleshooting such as checking free play of the motor, and looking for a burnt regulator. You could also use a 6v lantern battery to test the unit (after it is removed from the car of course).
Always disconnect the battery terminal connection first.
Early W210 Blower Motor Regulator Replacement DIY Here...
For those who have a weak A/C blower that does not seem to change speed despite where you set the controls, here is a DIY to replace your Blower Motor Regulator.
At some point in the run of the W210, Mercedes-Benz decided to redesign the unreliable regulator. Unfortunately, the redesign included the entire blower assembly, so if you try to buy a replacement for the regulator from your dealer you will be sold a new blower assembly, a new housing, and the new regulator.
However, a former local wrench in the Atlanta area described adapting the blower motor regulator from a W140 (S-Class) to the early W210 (The later W210 has a totally redesigned part and only a new regulator is required if your part fails). Here is my interpretation of the adaptation:
First of all lets see where the part is located. Look under the passenger side footwell and look up. This is what you will see:
Remove two phillips head screws and the cover can be pulled off toward the seat. With that cover off you will see the blower motor cover:
Remove the five Torx screws(T-20 i believe) and you will expose the blower motor and harness near the corner to your right nearest you:
Disconnect the harness by pulling apart. There was no locking mechanism that I could find. After releasing the harness, remove four torx screws(Same size as the cover) and the blower assembly will drop down. If you look up the void left by dropping the blower you will see your A/C filters. Check their condition and replace them if they look dirty at all. I had replaced mine recently and they still looked new:
Take you blower assembly to your work table and you will see the blower motor regulator attached to the blower motor with two torx screws of the same size as all the others you removed earlier. Here is a picture of the old and new regulators. I purchased mine from Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips
Remove the two torx screws and cut your OLD harness right next to the OLD regulator. You will be cutting four wires: a thick black one, a thick blue one, and two thinner yellow and red ones:
I stripped most of the black sheath covering the three wires on the OLD harness to give myself room to strip the insulation off of the three wires I will need to splice.
Next take your new harness and regulator. You can go ahead and connect the blue wire with the spade connector to the blower motor. You will need to remove the blue wire coming from the OLD harness from the motor to do this. Throw the old blue wire away. The OLD red wire attached to the blower motor will stay. This is what it will look like:
Now cut the four wires going into the NEW harness connector(Cut the wires as far away from the new regulator as possible). Note that the blue one goes straight to the blower motor so it will not be cut. You will need to cut right next to the connector box in order to leave enough wire to splice to the OLD harness. When you cut the four wires, you can discard the thick red wire. The other three wires will be spliced to the three wires (black,yellow and red) from the OLD harness. Here's how i spliced and soddered mine:
I then taped each wire with electrical tape, put a very thin coat of the included dielectric grease to the new regulator, and mounted the new regulator with the two new torx screws supplied with the new harness:
I then installed it under the dash in reverse order and started the car up. Woo hoo! It worked. Lots of $$$ saved.