W204 08 reg Blower - Fuse or blower motor

[JonTallis]

Update....
Cleaned all terminals.
Checked the fan is free to spin when installed - all OK
Checked voltage into the resistor - full 12v
Checked for voltage on the 3rd wire on the input plug which I presume is the speed signal. This varies from around 4v on minimum fan to 12v on max fan. No idea if this is right but it seems pretty logical.
Voltage out to fan is all over the place but not more than 2.5v so fan not running.
Have tested with both the old resistor and new (Chinese eBay) one.......didn't want to spend £150 on a pattern resistor or £300 on a Merc one until I knew that was the fault.
So........either both resistors are faulty or the input voltage from the fan control is haywire.....my money's on the former but if anyone can confirm what the input signal / voltage to the resistor is supposed to be that that would confirm......

 

[johnsco]

Prestige Allparts came straight back to me first-thing this morning.
They have quoted £35 + VAT + postage - - - Tried and tested with 3 months guarantee.
I have used them before with good results, so I have ordered the part.
Hope for the best !!
I'll let you know.

 

[JonTallis]

Thanks @johnsco, I've not come across prestige allparts before - I'll give them a try and hope you haven't got their last one! I presume that's a used part?

 

[johnsco]

I believe they have more than one of these heater blower units.
All used parts.
I've used them several times and found them pretty good.
I emailed my enquiry yesterday (Sunday) at around 4.30pm.
I got a phone quotation with email confirmation at 8.15am this morning.
There are cheaper on the Bay .... But .... I trust them on past performance.

 

[Pontoneer]

Thanks for response. I've removed the resistor and blower from car. On the resistor I checked continuity across input and output pins no 1 showed continuity but 2 didn't. To be fair I have no idea if on resistor what continuity should show. I also wired in again and tested and no output from resistor to blower. Not sure I can check anything else to ensure its resistor and not blower. Resistor is circa £150 blower £140. Massive variation in prices ecp want close to £400 for the former!!!!

A breaker is the answer to that , just take a meter along and test the resistor pack before handing money over .

 

[JonTallis]

Well Prestige Allparts came good. Used resistor arrived today, fitted and fan working perfectly. New part from Amazon was U/S.

Having worked through this, I think the following is a reasonable way to diagnose a non-working fan and can be done without removing the components from the car.
Remove the fan shroud behind the battery and check fan is free to turn.
Check input voltage to the resistor - should be 12v - if not you have a power supply or wiring problem.
Check signal voltage to the resistor. Should vary between around 4v at minimum fan to 12v at full fan. If different you have a control unit or wiring problem.
If the above are OK, check the output voltage to the fan - should be 12v at full fan. If this checks out and fan still not working, you have a dead fan.

Hope this helps others

 

[JonTallis]

Well....looks like I spoke too soon. Fan was working perfectly yesterday.....not working at all this morning.....I'm at a loss now. Think I'm going to have to just bypass the resistor and run with fan off or on full until I can get the car booked in to Mercedes....and brace for a big bill

 

[johnsco]

Well....looks like I spoke too soon. Fan was working perfectly yesterday.....not working at all this morning.....I'm at a loss now. Think I'm going to have to just bypass the resistor and run with fan off or on full until I can get the car booked in to Mercedes....and brace for a big bill

Oh No, Jon.
That's very disheartening.
I've received my fan+resistor unit from Prestige and I'm going to try fitting it this morning - Despite the very cold weather.
[I hate the cold !!]
Wish me luck !

 

[johnsco]

Very bad news.
In an hour in the freezing cold ...
I connected the replacement fan motor.
Guess what - Mine doesn't work either.
[Lessons in foul language at this point !!!!]
I'm going to check the connections and voltages ... as per JonTallis's post.
Is there another control module ?
Is there a fuse ?
Where and what should I look for ?
Any help will be welcome.

 

[JonTallis]

Very bad news.
In an hour in the freezing cold ...
I connected the replacement fan motor.
Guess what - Mine doesn't work either.
[Lessons in foul language at this point !!!!]
I'm going to check the connections and voltages ... as per JonTallis's post.
Is there another control module ?
Is there a fuse ?
Where and what should I look for ?
Any help will be welcome.

@johnsco, sorry to hear that...let us know what you find when you check voltages....

 

[johnsco]

Hi JonTallis.
Yes - That was very disappointing.
I will check out the voltages.
All round here is pretty-bad snow, so it will have to wait a day or two.
I've nowhere warm to work

It's MOT test day tomorrow for the W211 E280 cdi Estate.
It's going to need one puncture repair and one replacement rear tyre (side-wall damage).
Oh Joy !!
I'll be back when I've checked out those voltages.
Does anyone here know if there is a fuse to check ?
Surely - There must be.

 

[Tuna212]

Hello I have just had the same issue on my 2015 c300 w205. Fan was running slowly then died. I bought a replacement motor from a breaker and after much cursing replaced it tonight in the freezing cold. Not working still! Any ideas where the fuse is I need to check on this? There's a couple of 30A ones in the passenger fuse box which I changed but made no difference. Also not sure if this model has a separate resistor or it's built into the unit itself? Appreciate any help on this I desperately need car up and running.

 

[Tuna212]

Looks like the resistor is built in.

Link

So should i check voltage on motor connector terminals with fan switched on? Should it be 12V?

If no voltage does that mean a fuse could have gone? Any ideas where this might be?

 

[johnsco]

I've been struggling with these same questions for our year-2005 W203 C200 SE Coupe.
The weather has been so dreadful that I've been unable to get any further with it.
My big question is this .....
I've changed the blower motor + resistor (a combined unit) and it has not cured the problem.
This unit claims to be tested good
Can anyone help with the question of fuses ?
I've done some research and I'm going to check fuses Nos. 30 and 41.
Does anyone have any better information ?
I'm going to check out a few more things when it warms up a bit.

 

[Tuna212]

Sorry to hear you're having the same issues.

This morning I tested across points 1 and 3 on the connector and there was 12V. I also tested between 3 and 4 and there appeared to be 9V.

Does this suggest that there is power to the motor and fuse is good? Any ideas what next port of call is here?

 

[johnsco]

Pins 1 and 3 clearly supply the current to the motor - probably via a controlled resistor.
Pins 2 and 4 will be the control voltage that controls the resistor to vary the current to the motor.
What you are measuring are the voltages with no load.
When you plug in the connector, the load may kill the voltage.
Hard to measure it when the plug is inserted into the unit.
That's my guess.
Does anyone have better information ?
I'm hoping to have a look at mine this weekend when the weather warms up a bit.
It's still below zero round here and my age (77) and health (diabetic) rather limits what I can do in serious cold.

 

[Tuna212]

Thanks. Would there still be voltage if the fuse had gone?

 

[johnsco]

I'm almost certain that a blown fuse would mean NO VOLTAGE.
I say "almost", as it's easy to be deceived with Canbus circuitry and disconnected connectors.

 

[johnsco]

This afternoon the temperature increased to zero.
As per my post #34, I checked out the fuses.
Fuse No. 30 has burned out and has taken the fuse holder with it.
This is clearly the 40 amp fuse that is in the supply to the blower motor


The light was failing (and not only the light).
The fuse socket is doubtless goosed.
I should be able to outrig a bypass fuse.
Job for tomorrow.

 

[johnsco]

The fuse No. 30 has various designations - Depends where you look.
On one site it is listed as:

40A Heater air circulation unit
Sounds about right.

The cover at the side of the dash is a pig to get off and on without breaking it.
Clever these German engineers.