HI all, I went out in the car last week as usual and when I tried to put the blower on to full to demist/ defrost the screen.........nothing !! I had a 30 mile journey to make so carried on. Once on the motorway there was enough worm air coming through the vents to keep the screen mist free, but no blower. On trying to find a fix, most popular was a faulty blower motor, I firstly checked the fuses and all seem to be fine so I ordered a new blower motor , which arrived today and I fitted it but nothing - still not working so I think there is nothing wrong with the motor after all. Could the next most likely thing be the Heater blower Regulator and is there any way to test it ?

 

Disconnect connector to blower, start car and turn AC on. Test connector pins for power using voltmeter. If there’s power blower motor is malfunctioning. No power, regulator may need replacement. Disconnect connector to regulator. If there’s power, reinstall the connector. No power, there may be a problem with the control unit in dash.

 

Many thanks sir, I will try this tommorow,

 

You did good by installing your replacement blower! The original Bosch units run dry then get stuck.

​​​​​​Furthermore if your "resistor" (MOSFET modulator) voltage output checks out, then concider testing your HVAC module with a ODB2 scanner.

 

OK, an update. I tested the blower motor by taking a fused live and a earth wire and connecting then to the plug coming from the motor and hey presto, it is working fine. I then connected the multi meter to the output plug from the blower fan resistor and had no reading at all , so then connected the multi meter tothe input plug and had a reading of 14.4v which I think means the resistor is the faulty part. I have ordered a 2nd hand Mercedes (Behr) resistor that has been tested and is from the exact same model car as mine and all part numbers etc match, so hopefully it will arrive in a few days and I get it installed and it works. I will confirm when it arrives.
Thanks for all the help.

 

Great job! You are getting a replacement for your toasted resistor module.

Now take this opportunity to either replace the cabin filter or remove it to ensure a strong air flow can cool the resistor at all time.
It gets hot by radiating the power caused by the dropped voltage.

 

Hi all, Just an update , I bought a 2nd hand resistor relay which was a original part from a sister car to mine, got it for £25.00 at an online auction site , fitted it and BINGO evrything works fine, got my blower back , so all good. Thanks for the help.

 

In my 2014 V6 E350 4MATIC the blower fan quit working. Tested Auto, Manual and Max Def and Max Cool. I can hear the vents opening, but no fan is blowing the air.

My first thought was a fuse...but the fuse map included (in the roadside tool kit) is of little help as there is nothing listed. Is there a fuse? It seems like it should be obvious.

Went by the dealership to ask....willing to set a 1 hour minimum appointment to diagnose (Certified Pre-Owned, but not under warranty anymore). In my experience, I've never left the dealership without a $1,000 bill and think I should be able to check a fuse on my own...and the manufacturer should provide accurate diagrams for my model, not just every W212 model.

Anybody have any thoughts, suggestions?

Prior to the fan not working, I'd had the Max Defrost on when I arrived home and shut of the car. I normally turn the climate control back to Auto, so the fan isn't at max speed when starting again, but may have failed to do so this time. Later in the day...my wife drove and doesn't remember any fan noise, but on auto it's rare that we even hear the fan and it was a fairly mild day. Later that same evening, I took the car out at night (now colder outside) and noticed that there was no air movement.

Do I need to buck it up and take it to the dealership...knowing that it will be a complete heating system replacement more than likely, whether it needs it or not?

Thanks,

Damon

 

I think you should be golden quickly.

I'd concentrate on testing the "resistor"... 85% chance it being toasted from high heat. ​​​​


"resistor" come in different styles

If you like/need high-speed, you can bypass the resistor to supply full line voltage to blower if you need defrost or heat for winter driving up North.
​​​​​​
Enjoy the front passenger footwell

 

I have a 2015 E250 Bluetec W212 and the blower stopped working. I replaced both the blower and the resistor and the blower now works BUT it cuts out after about 30 seconds and comes on again and off again until it no longer comes on until I shut the car off and restart.
It could not be a fuse since a fuse does not reset but a relay does. So I think it is a relay. Can someone tell me which relay(s) to check or is it possibly the climate control module in the dash? Any guidance would be appreciated.

 

you'd save your time & money by using a good scanner - The ballast is electronic.

For some reason these cabin blowers are built with extremely tight sleeve bearing they can hardling spin... read high current!!

Lubricate the shaft bearings will help lower the current into normal range.

 

The scanner did not show any faults. After installing the new fan and resistor I checked the old fan off line and it was fine. So I plugged it in the car - without removing the old fan - and the problem I described persisted. So I knew the new fan was OK.
The resistor has a black plastic front and a metal back cooling plate. The metal back cooling plate of the old resistor was crudded up so I scrubbed the outside with a brush soap and warm water. In so doing I saw that the black plastic front and the back metal cooling plate of the resistor were held together with 4 clips (1 on each of the 4 sides). I removed these clips and it came apart revealing the internal circuit board. On visual inspection, this circuit board appeared fine however when I removed the circuit from the metal back of the resistor case, there was scale build up between the back of the circuit board and the "pad" that is on the inside of the back metal cover. I carefully removed this scale from the back of the circuit board and the face of the pad on the inside of the back metal cover and reassembled the resistor. Without removing the new resistor from the car I disconnected the 2 electric cables plugged into it and plugged them into the cleaned up old resistor and voila!!!!! Problem solved!!!
I will drive the car a few days to be sure everything continues to work ok before putting everything back together but it was now obvious that the new resistor I bought on Amazon was defective. It was obviously the correct one as the add said it replaced the Mercedes Part No. as shown on my original resistor. Go figure. If the cleaned up old resistor fails again I will only buy the OEM original from M-B and save a lot of time $ and frustration. Hope this helps someone else. Cheers.

 

I am curious, what is the P/N on your original blower speed controller ?
Some says resistor used, some say that is PWM unit........ mine is A212 870 21 10

Do you have photos of the internal when you tear it down ?
I would love to see it for future maintenance need, if any. Thanks

OP wrote :
"The metal back cooling plate of the old resistor was crudded up so I scrubbed the outside with a brush soap and warm water. In so doing I saw that the black plastic front and the back metal cooling plate of the resistor were held together with 4 clips (1 on each of the 4 sides). I removed these clips and it came apart revealing the internal circuit board. On visual inspection, this circuit board appeared fine however when I removed the circuit from the metal back of the resistor case, there was scale build up between the back of the circuit board and the "pad" that is on the inside of the back metal cover. I carefully removed this scale from the back of the circuit board and the face of the pad on the inside of the back metal cover and reassembled the resistor. Without removing the new resistor from the car I disconnected the 2 electric cables plugged into it and plugged them into the cleaned up old resistor and voila!!!!! Problem solved!!!"


Mine



.

 

A212 870 21 10 is the P/N on my unit and is the P/N I ordered from Amazon. Sorry no pictures but I can see the clips in your pictures. It is easy to pop them off with a tiny flat screwdriver and the entire internal circuit board comes out easily in 1 piece. Then you will see the pad (and possibly the crude) on the back side of the circuit board and the top side of the pad that is attached to the inside of the metal back plate. Good luck. It was a simple fix for me.

 

Okey, next time I will teardown for fun...., thanks.

 

MS your friend has been there:
This is a good PWM control Module, not a hot cheap resistor.
Good for scoping

It's like a baby radiator blower with duty cycle. Presumably pulses of 12volts.
PWM preserves good torque instead of 4VDC out of a hot resistor: no torque!

I don't know what makes this fail beside the dry bearings famous for sqweeking... High current, high heat.

They're really trying hard to develop extra service needs. Of course filter needs air flow to prevent ballast PWM from acumulating extreme heat.

 

I am just wondering about the :there was scale build up between the back of the circuit board and the "pad"
Its closed system, should be clean inside right ?
Or the heat/thermal paste gone bad ? I read they have life span too.

 

I saw evidence of water on top of my ballast. Inside it's likely dried silicone on top of MOSFET.
These parts are built carefully...

I remember my ballast looked like a solid module not loose pins in sight or capacitors leaking across unprotected traces.

I'd say failure rely on:
#1 filter no air circulation
#2 dry sleeve bearings
#3 oxidized overheated harness