I have seen this problem around the forum and no one has seemed to come across a real fix. I think this is the true fix for it.

https://www.benzworld.org/threads/w2...bulbs.2141945/

On my Crossfire, the blower speed would change speeds by itself and even turn on when it was set to venting only, where the blower and A/C light should be off. I already replaced the blower resistor and it did not make a difference.

I tired the fix myself. I desoldered the potentiometer and soaked it in isopropyl alcohol. I also separated the metal backing and plastic slightly using a pocket knife to make sure the alcohol got inside. I turned the **** to clean inside and thoroughly dried the part before resoldering it. Now the blower speed seems to work normally.

There may be a way to remove the temperature wheels so you do not have to desolder the poteniometers for the temp wheels to get to the blower potentiometer, but using an allen key on them did not work for me. It may mess something up if you force it. My wild guess is that the white plastic with the allen key hole is a shaft that snaps in when assembled. I do not see why it would fit an allen key in that case though.

A new potentiometer would be better than cleaning but I am not sure if they are available. The brand is Piher and there is an "X" on the bottom of the front side. The number stamped on the side is 4k7344ME.

Hope this helps someone!

 

Brasstacks2, good write up thanks. Here is another on the same subject CLICK

 

The first part of the part number is to indicate the value of the potentiometer 4K7 means 4700 ohms resistance.

 

Way back I looked into replacing the potentiometer but it would have to be custom ordered and the only one with the true specs is Bosch if I am not mistaken.

 

Curious how you came up with that?


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Its the standard way of identifying electronic component values that cannot be colour coded, resistor bodies are colour coded, hence no requirement for the lettering.

 

brasstacks2 - This DIY by CL770 is probably the permanent fix to the intermittent HVAC problem on the Crossfire. From what I can remember, everyone that has performed this repair solved the HVAC issue in their car. Attached is a PDF of his procedure.

 

I did try the fix from CL770 before but it did not work for me. As for the potentiometer, I found a couple of very similar Piher models that are 4.7 k ohms on the Mouser distributor website. I'm not familiar enough with electronics specs to figure out if either of them would work though. Piher offers the PT15 potentiometer in long life versions. I think they are 10,000 and 100,000 cycle rated.

 

It did not work for me. I followed up with CL770 later on and he had the same problem again.

 

I have been in touch (contact) with the manufacturer in Spain for the potentiometer. hopefully they have stock or can offer a suitable alternative to us.

 

So can we say this is not the answer?
If so I shall remove it from my list of solutions to Crossfire problems.
I had my unit out and made the mod to make it go into the connectors all the way but could not see how it would fix the problems people have.
Why didn’t he come back and say it did not work after all?

 

Bit confused now guys as to what we are talking about regarding the blower problems. What are we saying doesn't work/solve the problem?

I ask as I have just started having similar problems and don't want to waste my time with something that has been shown not to be the solution.

Cheers

 

They are talking about a possible intermittent connection internally in the control module ( thing with dials and ***** )
Dave ( onehundred80 ) voiced doubt that this is truly a fix.
The jury is still out.

 

I take that to be the 18 way pin header not seating correctly with the other PCB and the units plastic frame causing a foul condition.

 

You take it right. I think it is an issue, but not the answer to everything.

 

I have been following the write up by Jefferyallison with respect to the "Blower Motor and Resistor Bench Test". To be honest this is a very fine write-up and should be followed by all in a similar situation.

I have learnt the following so far:-
1. My blower motor runs fine most of the time so can ignore a seized up motor, albeit the motor brushes may be worn. The correct voltage is being supplied across the red & brown pins of the 3 pin connector on the "resistor/regulator" cable.
2. I have no debris in the motor housing.
3. I am unable to test the PWM (resistor/regulator) unit to see if it is functioning correctly.
4. I have found that the "Control Module Output" (pink wire with white stripe) voltage fluctuates between 7.5v and 3.0v when the unit is monitored in real time. This may indicate a bad soldered joint, a damaged cable, a component that provides the stepped voltages via the pink wire is suspect, a worn potentiometer or another component on the control module circuit board.

The only answers I have found would be to:-
1. Change the PWM (resistor/regulator), easily done and only £25 / $30 for a new one.....but i don't think that's the problem.
2. Re-solder any soldered joints on the "control module"....easily done as I work with PCB's. Removing the unit from the car is another issue, can anybody provide a write up especially with pictures to show how it is done?
3. Continue to use the car as it is....we have had our 5 hot days in the UK so it probably wont be needed for another 12 months.

Thanks for reading my comments, have I missed anything else out?

Cheers
Mark

 

[QUOTE=THETESTER;942387]

Mark

4. I have found that the "Control Module Output" (pink wire with white stripe) voltage fluctuates between 7.5v and 3.0v when the unit is monitored in real time. /QUOTE]



I believe that output is exactly what you want.



.

 

I respectfully disagree, the voltage should only change when the dial setting is adjusted, ie from a setting of say 2 slow speed, up to a setting of say 5 full speed. Random changes in voltage to the PWM (resistor/regulator) via the pink wire would cause the blower motor to run erratically, just as we are all seeing.

The voltage should be constant for each dial setting. I however confirm that I did not make it clear that my comment (item 4) was to state that the voltage was fluctuating without any change to the blower speed dial setting.

Kind regards
Mark

 

Errrrr, trust me when I say you cannot respectfully disagree if you didn't make it clear you didn't turn the ****. Good luck with your fix.


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GraphiteGhost.

You are 100% correct. I made the error in not checking my post fully before submitting. No offence intended.

As an aside, I believe I am correct that the voltage should be constant for each setting on the dial. I have never found any past postings that confirm or deny this. If other people have the same issue, especially on the pinkwire, why do they change the PWM (resistor/regulator)?

Kind regards
Mark