W204 08 reg Blower - Fuse or blower motor

[Tuna212]

Hi johnsco, unfortunate that the fuse housing has been blown along with the fuse. Not good! Hope you get it fixed.

So after testing I reassembled the blower motor and today had to drive for 2 hours.

About half an hour in blower comes on for around 30s, then goes off. Half an hour later it comes on and stays on for the remainder of the journey.

Could this be a loose wiring connector? Also, might be a coincidence but I drove through some pretty deep flood water around a week ago. Maybe moisture somewhere had caused an issue?

I am booked to take it to mercedes on Thursday but have another 2 hour journey on Wednesday so will see what happens on that before I take it in. Very strange!

 

[johnsco]

I accessed the fuse panel in the right-hand end of the dash.
The fuse holder block can be removed by undoing one screw.
Fuse No. 30 is the damaged position.
I snipped off the wire that goes from Position 30 to the blower motor.
I outrigged a bypass fuse and connected it to a live position.

The yellow sleeve is a piece of "shrink-on" sleeving for protection

See photos.





Success - The motor runs and the controls function properly.
I tested both the original blower motor and the one that I bought from Prestige Allparts.
Both come with the control resistor built into the module.
Both tested 100 per cent OK.
I refitted the original unit and now have a tested spare on the shelf.
A good day.

 

[JonTallis]

@johnsco , looks like you have made some progress....so have I... apologies for the absence..I measured the voltages into and put of the resistor and noticed an interesting thing, the resistor seems to trip out if the fan doesn't run in response to voltage (I guess either on over current or lack of a voltage drop), so whilst waiting for a new second hand motor to arrive I took mine out, disassembled it from the housing and gave it a good look at. Smoking gun was no witness mark on the commutator from contact from the brushes. Brushes were very worn and lots of carbon dust around, however a good dose of brake cleaner and a blow through with compressed air and it's working! Not sure for how long but long enough for the new motor to arrive.
Link to video...

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[johnsco]

Thanks for this JonTallis.
It does appear that the resistor is "tripping out" in some way.
At least you do appear to have motor-supply voltage and control voltage.

I have been supplied how fast the fan motor rotates - Especially when I press the button to clear the front screen.
I did wonder about the life of the DC motor brushes.

 

[Tuna212]

Just an update on the issue on mine in case anyone has a similar problem. I ended up taking car to mercedes for diagnostics. £1200 later they found the issue. There was an electrical anomaly causing power to feed the motor when it shouldn't have been. Hence intermittent operation. They got into the guts of the wiring under dash etc to try and isolate the fault. Ended up there was corrosion inside the plug and socket for the AC compressor. They cleaned up the terminals and this has resolved the issue. Recommended changing out the AC compressor to prevent recurrence but need to save a bit of cash for that!