Heater fan (blower) stopped working -- Solved

[steveq]

The heater fan on my Merc E220 CDI S212 stopped working recently.

The A/C switch looked like it worked perfectly with the lines displayed and increased as I moved the switch -- just nothing from the fan and no OBD error codes either.

I had another problem with a coolant leak which was a higher priority. I documented resolving that on a separate thread.
Now that that was sorted, I started into the heater fan issue.

I thought that it might be the fan itself. The blades of the heater fan are visible from the engine compartment when the plastic cover over the main battery is removed. The fan blades can be seen and it is possible to get fingers in to give it a spin -- don't have the key in the ignition when trying this!! I thought it might free up the electric motor but it made no difference.

I then removed the heater fan -- it is removed by taking the cover off the passenger side cover (where the pollen filter is). You have to lie on you back and look up behind the glove box to see the fan and other parts.
The fan is removed by pulling a little plastic piece on the fan and twisting the fan motor. There are two cables attached to it which have to be disconnected. One is a connector with two pins which is the fan power lead that is wired into the fan and the other is a connector with four pins that is attached to the heater regulator but the cable is just clipped onto the fan motor.
Here is a link to a video -- it is from a LHD car but it is much the same:-

I removed the blower thinking it was faulty.
I attached a small 12 volt battery I had to each of the two pins using small crocodile clips -- I don't think it matters which way the +ve and -ve wires are connected.
The heater fan roared into life.

That meant that it was the regulator (sometimes called the resistor) that was probably faulty. That is situated right beside the fan motor with the two connectors mentioned above. They just pull out of the regulator.
That is much easier to remove with just 2 torx screws holding it in place.
I understand that it gets quite hot in operation and there is a gap where some of the air from the fan passes directly over it to cool it down.
This is what it looks like:-


That is the side you can see from the footwell. It is about 4 inches long by 2 inches wide.
The other side is metal with dimples in it to help dissipate the heat, I presume.

I tested my one to check the resistance -- all seemed to read zero on my meter for every pin of the four pin connector to either of the two pin connector which is no circuit -- definitely faulty (I understand).

I bought a non-Merc part and fitted it.
The heater motor works perfectly -- the fan speed changes correctly.

In hindsight there was no need to remove the heater fan/blower motor. I could have tested it in-situ and saved a bit of time lying on my back in the passenger footwell -- but just think of the fun I would have missed!!??

I don't know whether the fan motor or the regulator/resister fails more regularly but in my experience, it is definitely worth testing the fan using a 12 volt supply prior to taking it off and (if the fan works) checking the regulator.

 

[Blobcat]

A lot of heater fans fail (not just on MB) due to water ingress due to blocked scuttle or battery drains. The water goes into the heater then gets to the bottom bearing of the blower motor / this thread corrodes and seizes the fan.

 

[peterws1957]

The heater fan on my Merc E220 CDI S212 stopped working recently.

The A/C switch looked like it worked perfectly with the lines displayed and increased as I moved the switch -- just nothing from the fan and no OBD error codes either.

I had another problem with a coolant leak which was a higher priority. I documented resolving that on a separate thread.
Now that that was sorted, I started into the heater fan issue.

I thought that it might be the fan itself. The blades of the heater fan are visible from the engine compartment when the plastic cover over the main battery is removed. The fan blades can be seen and it is possible to get fingers in to give it a spin -- don't have the key in the ignition when trying this!! I thought it might free up the electric motor but it made no difference.

I then removed the heater fan -- it is removed by taking the cover off the passenger side cover (where the pollen filter is). You have to lie on you back and look up behind the glove box to see the fan and other parts.
The fan is removed by pulling a little plastic piece on the fan and twisting the fan motor. There are two cables attached to it which have to be disconnected. One is a connector with two pins which is the fan power lead that is wired into the fan and the other is a connector with four pins that is attached to the heater regulator but the cable is just clipped onto the fan motor.
Here is a link to a video -- it is from a LHD car but it is much the same:-

I removed the blower thinking it was faulty.
I attached a small 12 volt battery I had to each of the two pins using small crocodile clips -- I don't think it matters which way the +ve and -ve wires are connected.
The heater fan roared into life.

That meant that it was the regulator (sometimes called the resistor) that was probably faulty. That is situated right beside the fan motor with the two connectors mentioned above. They just pull out of the regulator.
That is much easier to remove with just 2 torx screws holding it in place.
I understand that it gets quite hot in operation and there is a gap where some of the air from the fan passes directly over it to cool it down.
This is what it looks like:-
View attachment 87045

That is the side you can see from the footwell. It is about 4 inches long by 2 inches wide.
The other side is metal with dimples in it to help dissipate the heat, I presume.

I tested my one to check the resistance -- all seemed to read zero on my meter for every pin of the four pin connector to either of the two pin connector which is no circuit -- definitely faulty (I understand).

I bought a non-Merc part and fitted it.
The heater motor works perfectly -- the fan speed changes correctly.

In hindsight there was no need to remove the heater fan/blower motor. I could have tested it in-situ and saved a bit of time lying on my back in the passenger footwell -- but just think of the fun I would have missed!!??

I don't know whether the fan motor or the regulator/resister fails more regularly but in my experience, it is definitely worth testing the fan using a 12 volt supply prior to taking it off and (if the fan works) checking the regulator.

A good bit of research and fettling there. I had the same problem and it was a relatively easy but fiddly fix. I was warned off none OEM regulators by posts on US forums and advice from my trusted indie. Plenty of cheap units on eBay, but the general consensus was that they don't last long at all. And the cheap blower motors on eBay are awful!

 

[steveq]

A good bit of research and fettling there. I had the same problem and it was a relatively easy but fiddly fix. I was warned off none OEM regulators by posts on US forums and advice from my trusted indie. Plenty of cheap units on eBay, but the general consensus was that they don't last long at all. And the cheap blower motors on eBay are awful!

I was nervous buying a non-MB regulator but the one I bought was significantly cheaper than the genuine article and has a two year warranty. The one I fitted cost about €100 including postage. I think genuine MB ones are over €300 new. I see that a new genuine MB blower motor is around €500!!

I opened up the old one -- very easy to do by just levering off the four brass coloured clips that you can see in the photo. I thought I might see a component inside that would look like it had overheated which I could replace. There was nothing obvious but I haven't given up hope. I'll keep the faulty one and hope that some more knowledgeable soul might post a video showing how to repair it.

 

[peterws1957]

I was nervous buying a non-MB regulator but the one I bought was significantly cheaper than the genuine article and has a two year warranty. The one I fitted cost about €100 including postage. I think genuine MB ones are over €300 new. I see that a new genuine MB blower motor is around €500!!

I opened up the old one -- very easy to do by just levering off the four brass coloured clips that you can see in the photo. I thought I might see a component inside that would look like it had overheated which I could replace. There was nothing obvious but I haven't given up hope. I'll keep the faulty one and hope that some more knowledgeable soul might post a video showing how to repair it.

You seem to have bought a better one than the cheap chinese tat you seen on some sites. It will be interesting to see if it lasts but you have a 2 year warranty so some confidence there. It's annoying that as with most electrical equipment total failure can result from a cheap bad component costing a few pence.