I became a victim of the notorious intermittent fan motor operation. It was getting to the point I could predict it would NOT come on more than it would come on.

To test if it is actually the regulator or not is to use a meter and test for +6VDC on the center (white) wire of the fan plug to ground with the fan selector on five or it's highest setting. If you are getting the +6VDC but no power to the blower fan, then the regulator is defective and needs to be replaced.

I lucked out and it was misbehaving when I was testing it. If yours is working at that time, you may have to wait until another day to test it. The other way to tell is your HVAC Fan quits working randomly and then comes back on just as randomly.

The part was found at autohausaz.com

I've made a quick video of the replacement process. It's a bit over 10 minutes.


Enjoy!

 

What is it that makes these so pricey?
Would it be possible to repair one of these parts?
Lets get on the recycling wagon when we can.
I guess the guts are buried in epoxy but surely these are not rocket science.

 

onehundred80,

I actually mention in the video that I will be un-potting the unit to perform a failure analysis. If nothing else I will be able to document the existing circuit and formulate a replacement.

 

will this one work?

http://www.ebay.com/itm/New-HEATER-AC-BLOWER-MOTOR-REGULATOR-W208-W202-for-MERCEDES-BENZ/181142129416?_trksid=p2047675.m1850&_trkparms=aid% 3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26me id%3D343015929266495183%26pid%3D100011%26prg%3D100 5%26rk%3D5%26rkt%3D5%26sd%3D270815241647%26

 

It should, but as always, shop ebay at your own risk.

 

I skipped through the video and missed that statement. I suppose there are fixed resistors that are use in combination or alone and replacing them should not be a problem. A full speed fan would indicate a short in the series somehow. I have little knowledge on this stuff, so it is good that it is in good hands.

I want to open up a TPM sensor and replace the battery, as I always say "How hard can it be". LOL

I have a power washer in pieces and I cannot find why she blows fuses, how hard can it be? - too bloody hard at times.

 

I just can't believe they use RESISTORS to slow the fan down. What a half-assed way to go about it.

The Fan Module under the hood makes way more sense (pulse-modulated output) but I know is way more complicated.




I keep my top down a lot, so I guess mine will last and last since the fan in the HVAC is used less than most.....

 

I guess they use resistors, simple, cheap, and as it turns out not too reliable.
It is a potentiometer with fixed increments, I guess. The fins dissipate any heat and heat is probably the cause of the failures. These are all guesses on my part, how it works I have no real knowledge, but I would like to know. Lots of guesses but MMZ will let us know.

 

I'm sure heat is the problem - that's why I suggested the PWM idea.

But as far as simple, cheap and not too reliable - they could have used me.

 

Actually, I have the unit un-potted and found two MOSFETs, a single IC and quite a few SMD discrete components. It could be a PWM, but so far I can not find a datasheet on the component. I also found several BMW forums that had un-potted their failed fan controllers as well. Same component IC and part number. They are clueless as to it's specifics as well and have not been able to create a proper schematic.

I will be tracing all the components and reverse engineering a schematic during the week. More to come... stay tuned!

 

I did a quick study of the parts you mention, Googled them and now know that I am out of my depth. I did solve my door relay problem and found the SMD that was shot. That is about my limit, I'll leave this to the Time Lord.
For the record can you explain the workings, and include the dash mounted fan speed selector, I'm guessing, again, that this has the resistors in it, true or not?

 

I have to leave for work in a few minutes, but I can give my observations to date.

1. Climate controls output +0-6VDC based on the location of the climate fan selector.

From the Crossfire Specialist Student Reference Book, page 202 (PDF Page 214), it has the following ranges in five stages.

Stage 1 = 1.1 to 1.8 V
Stage 2 = 2.0 to 2.6 V
Stage 3 = 2.8 to 3.2 V
Stage 4 = 3.6 to 4.2 V
Stage 5 = 5.0 to 6.0 V

On mine I was getting a bit over 7 VDC on Stage 5. Not sure if that is significant.

That voltage is then used as a kind of throttle reference in the Regulator and a proportional 0 to 12VDC output is produced. I do not yet know if it is a PWM system or something else. The search continues.

 

Almost gotta be PWM, because if they are biasing the FETs to drop a few volts at several amps, those FETs are gonna get HOT. If it's PWM, the FETS are either ON or OFF - dissipating only a tiny amount of heat.

I sure hope it's a LONG time before I find myself digging into mine.

 

Good video and explanation.

Can you list the part number?

 

A picture is worth...

This is the OEM part I removed. This is the one I have un-potted and will be reverse engineering a schematic from. I took some pictures after I un-potted it, but they came out a bit blurry (shaky), so I'll take some new ones as I go.

EDIT: Okay, here is one of the blurry images and a few after I have cleaned up the bottom of the board. The top WILL be a challenge as it has that huge connector base. I can see that will take quite a bit of time to dig out the potting material. I will probably de-solder the three center pins and two side power connectors and remove them to make room to dig out and view the board a lot better. Looks like a two layer board, so it won't be too difficult to map out.

Enjoy!

 

This would be the point where I would say bugger it and toss it all away. Good luck.

 

So, I have not yet mapped out the entire circuit yet. The information I have gathered to date points towards this unit as being a simple linear voltage regulator controlled by the zero to six plus volts DC coming into the unit and providing a low to 12 volts DC to the fan motor. This is inefficient and wasteful (Heat).

It has been suggested that this module has some sort of function relating to temperature control of the system. IT DOES NOT!

The HVAC Fan is only low to high with five stages of speed adjustment. The ambient temperature and the temperature of the air moving through the system tells the HVAC system how much heat or cooling the air requires to achieve the desired temperature setting of the occupants.

From the Crossfire Specialist Student Reference Book:
From this we can deduce that the control is to the temperature of the air itself ultimately, NOT the fan speed. So the fan speed is occupant controlled only.

That being said, I am looking into a cheaper PWM control system that can simply replace this POS. BMW, Mercedes and of course Crossfires all suffer from these regulator modules dying. Funny that both BMW and Mercedes use the same ELMOS IC in their units.

 

Did you read this.

 

onehundred80,

I'm not quite sure why you referred me to that document. Yes, it has good information. Nearly all of which I have read previously. The problem here is that the "Fan Regulator" has gone bad and there are quite a number of owners in all three brand categories that have replaced more than one of these units.

I am making sure there is no special function for this unit other than translating 0-7VDC at low current (control signal) to 0-12VDC at high current (Fan operating power). When I talk about mapping out the circuit, I am referring to the internal circuit in the "Fan Regulator" itself.

I have come up with a simple PWM circuit that may be a cheaper solution. Without putting a scope on the fan power while it runs and see if it is already PWM, I have no way to confirm the ELMOS chip on the unit is a dual timer or something more complicated.

Anyone here able to put a scope on the fan power side of a working unit and see if it's pulsed DC or flat DC?

 

'Cos I did not understand it.