Tom Schneider

The other day my 2012 ML350 blower motor intermittently would not come on when selected from the climate controls. After researching this online some people have had problems with the drain hole becoming plugged and causing water to get into the motor and resistor board, but when I pulled my motor it was clean and had no water damage. I can connect 12v to the motor and it works normally when not in the vehicle. Doing further testing I have found that when the motor does not come on I have 3.9v on the input side of the resistor pack and zero volts on the output to the fan motor. When the motor works the input side on the resistor pack is 12v and the output to the motor is also 12v+/- depending on the blower speed selected. I have checked the continuity to the fuse block and all of the connectors at the resistor pack and motor and everything seems correct. Is their a relay under the back seat or under the hood that controls the voltage to the blower assembly or to the climate control system? When the blower is not working functions on the climate control seem normal except that the max cool, max defrost and the fan functions do not work to change the blower speed but the led displays change as if the climate control module is telling the blower to change speeds. Is there a reset procedure or diagnostics that can check the climate control system without a visit to the dealer?

I contacted my local dealer and they said that without connecting the vehicle up to the STAR diagnostic system to see if it has a code for a problem then they could not even give me an idea about the cost to repair the problem.

If anybody has had this problem or has any ideas to check that would be a big help.

Thanks

CA_Tallguy

I'm having this problem too over the last month. Thought it was fixed but today after going through a car wash I lost blower again. That makes me think that there is something to what you are saying about drain tube getting blocked -- does anyone have more info about such drain tubes and where they are?

I don't want to keep blowing up regulators and/or motors.

First time this happened I ordered a blower and regulator from a wrecking yard. I only installed the regulator because I figured that was the problem. I worked for maybe 1 or 2 trips in the car then it died.

Second repair attempt, I ordered a brand new regulator and installed that along with the blower that I hadn't used from the wrecking yard. The only thing I could think of going wrong on the first attempt was that maybe a bad blower motor caused the first and second regulators to go bad. I can confirm that the voltages were as described by the OP above when system was good/bad.

Above repair lasted a couple of weeks and today, a few hours after going through a car wash, I started up the car and NO BLOWER again. I want to pull my hair out!

This is happening in a GL350 but the blower and regulator are exactly the same in the X166 as W166. The used parts above came out of an ML, not a GL.

I'm thinking about just ordering another used blower and regulator from a wrecking yard because I can get that for $75 shipped. Then hope that these parts last a little while again and that if/when they go bad I can get some additional clues as to what may be causing this (such as if it happens after rain or a car wash etc).

The other option would be to go to the stealership and see if they can diagnose the root cause of this. This feels like a "ghost" in the system so it may get very expensive very fast at the dealer.... especially if they want to supply a new blower ($350 dealer price) and regulator ($350).

JoeHarmon

Sorry to bring back an old thread, but I have been chasing this exact problem. Replaced a couple regulators and a blower motor. Still intermittent functionality. Did you guys have any luck solving the problem?

CA_Tallguy

Yes! I'm sorry that I didn't follow up earlier to save you some trouble. There is a connection that gets loose and starts to burn up from shorting out. There is a service bulletin about it. Let me see if I can find it fo post.

HVAC BLOWER MOTOR INOPERATIVE AND DTC 912F87.pdf

AIR CONDITIONING IS INOPERATIVE, FAULT CODE 91EB11 OR 91EB15 IS STORED.pdf

AC BLOWER INOPERATIVE DTC 912F87 IN ACC THE FRONT BLOWER REGULATOR HAS A MALFUNCTION.pdf

JoeHarmon

CA_Tallguy, you are a gentleman and a scholar. Thanks so much for taking the time to respond and for sharing the PDFs. I have the W166, but I thought it was behaving like a bad connection somewhere and bet it is that. I will dig into it soon and check back in with what I find out. Thanks again so much!

CA_Tallguy

Note -- you might want to pickup a CarSoft scanner. These docs mention some fault codes so that might help you or someone else who comes across this trying to troubleshoot. But those codes are going to be deep and not available via a normal OBDII scanner. You need the Carsoft specific to mercedes or another specialized scanner.

pdeignan

Thanks, I'm having the same problem. Do you know if they ever did a recall for this?

cecpepper

Hi All, I recently purchased a white 2012 ML 350 4MATIC and motor blower went out. I thought it was water related as well but when no water was found I said "prepare for the screwing" let's go to the dealership. $498 later and them claiming they had to remove the passenger front seat and carpet they replaced a "wiring harness". After that point no more issues. Fast forward three months and compliments of a deer and the wire barricade on I-40 in TN I totaled that ML 350. Never fear, I bought another one. :-) Guess what... Have had this (new to me) blue 2012 ML 350 4MATIC and it is starting to do the same thing. What you can do is open the passenger door and slam your foot down on the floor board while the blower is set to level 7 high. You will find the sweet spot and the blower will cut back on. Or go to the dealer and spend $498. I'm beating the passenger floor board for another couple of months though...

Hope this helps!

Pepper

pdeignan

I’m still having the problem cause I won’t go to the dealer, but I’ve also problem down to a soft spot on the passenger side floor. I’ve got the panels off but trying to figure out how to get the carpet up. The spot is like 3 inches from the door, but doesn’t seem to be the connector that the service bulletin suggests. So thanks for your post confirming that my problem is the same. Amazing they haven’t done a recall on this!

Jay Holoway

I just purchase my 2012 ML350 two months ago. Today when I left the gym my heat would not blow from the vents. I drove to the maintenance shop and the guy was pretty rude, so I decided to Google and see if there was a simple fix. Your awesome, I rolled my eyes initially when I read your post. However, I decided what the heck do I have to loose. Sure enough one stomp on the passenger side floor and I had heat again. Thank you so much!!!

pdeignan

Its a loose connection under the floor board. You’re going to need to remove the front seat (disable air bag first), then pull out carpet. There’s a white connection box. The wires in it are male/female connections and one of them is loose. I literally used a pair of pliers to squeeze the connection tight again. That’s all it is. Putting the carpet back in was tricky, but I managed to do it by myself. Put seat back in and enable airbag. FYI, when I did it I didn’t know août the airbag part and the airbag light stayed on after I put everything back together. My mechanic had to fix that for me.

APEREZ

Do you know what parts are needed for this repair? The dealership of course says they dont know what im talking about and want me to replace the whole harness. Also is there a diagram or video on how to remove the front seat and carpet?

pdeignan

I didn’t need any parts for this. There are 4 bolts to remove the seat. Two in the front, and two in the back. So, I moved the seat all the way back, used a ratchet to remove the bolts in front, then moved the seat all the way up to remove the rear bolts. Of course there are wires Connected to the seat which un clip, BUT.... if possible don’t remove them, and just position the seat back a little once you remove the bolts, or in order to access the carpet. THIS IS BECAUSE IF YOU REMOVE THE WIRES, IT WILL DISABLE THE AIREBAG. I believe there is a small panel to remove before you can remove the carpet. Also, there are some panels under the dash that you have to unscrew as well. At this point, just pull the carpet out. It’s a lot easier to take out than it is to put back in. After the carpet is out, there is a gray plastic connector (harness) by the floor board in front of the door. I believe there are three wires going into it. Gently pull each wire out, you’ll see a male and female connection. One of those wires will have a loose female connection. (This is the source of the problem). I literally used a pair of pliers to tighten it, and reconnected it. That’s it! Test to make sure everything works and then put it all back together. Again, putting the carpet back in is a challenge, cause you have to stuff it back into all the crevices.

NOTE, if you do have to disconnect the wire under the seat, you’ll need to disable the airbag first. (I don’t know how to do this, my mechanic had to fix it afterward). Maybe google that if you have to. But again, try to avoid.

it’s unbelievable to me that Mercedes never recalled the vehicle over this. Good luck, if you have any more questions, I’ll help best I can.

marcd7tx

I was able to do this repair on our 12 ML350. I didn't have to remove the seat. The problem lies where the floorboard (where your right foot would be) goes up into the dash. You just have to pull up hard on the carpet. You will notice one of the wires is burned. I cut the bad part of the one wire, and used a wire connector to reconnect the wire. It's been a couple of years since I did it, but it was not that hard. I also went through a new motor and new regulators to no avail. Mercedes did not have a heavy enough gauge wire to handle the current.

steveyfly

are the wires on the passenger side or drivers side I’m in the Uk with a right hand drive ml 250 bluetec sport And do the covers remove
easy just wondering where to start any help appreciated

marcd7tx

I imagine that RHD cars are going to have the blower fan on the left hand side. If you have ever changed your cabin air filters, that will confirm which side your blower motor is on, and thus the wiring harness.

The covers should "pop" off. You will need to remove the under the dash plastic cover which is held in with 4 or 5 hex screws. GLWR

steveyfly

Hi Marcd cheers for the quick reply yes I know where the four screws are and the panel should drop down and pop pout hopefully I will have a go when I get a good few hours free and hopefully pop the panels off I’m presuming the left hand side small panel will pop out the the ones along the sill that meet the carpet do also . Would I be right in thinking that .

marcd7tx

Yes. Pull back the door insulation and carefully pry the side kick panel out of place. Trace the power wiring from the fan down into the footwell and you should see the compromised portion of the wire somewhere between the footwell angles up into the firewall area. You don't have much "play"/slack in the wiring so be careful not to cut too much out, unless you want to place additional "patch" cable in place.

marcd7tx

I did find a good post on this forum or another forum where someone posted photos of his repair. It's been a while, so I haven't researched it.

marcd7tx

Ah, now I remember! I ended up taking either the negative or line wire and pin out of both of the connectors because it had shorted/melted, You should see where it's charred. Then bypassed the connector of the wire of the bad pin and just spliced it direct. So in other words, take the bad wire out of both ends of the connector and direct connect them. I think the issue was the pin was too small to manage the current going through it.

steveyfly

I’ve sussed an easy to access to the cables the plast kick comes off no probs as you said thank you although my heaters are back on I’ve not cut nothing yet the connector looks ok and wires look ok I’ve nipped the female connectors so the males are a good tight fit so I’ll see how it goes Fingers crossed It thanks for your advice and everyone else at leased I saved taking the passenger seat out . And I’m hoping things are good now no doubt il be in there again

Brk23

Thank you so much men!

I just got my ML home, buying it second hand and the fan stopped..

good to have you guys, THANKS !!!

Oleg Olekshii

As it happened to my 2012 ML (Error: 912F87 in AC system), thanks to this thread and all tips posted, I've hoped to fix it without braking the budget.
So, after hitting the passenger side floor and blower started working for some time, I decided to take further actions to fix it permanently - see attached.
- Do not disconnect wires from the seat but just remove 4 bolts and tilt it back;
- Fixed by puling both ends of problematic wire from connectors and connecting it using "Wago 221-412 Lever-Nuts 2 Conductor Compact Connectors";
- Locate/place fixed connection higher at the side but not under the carpet to monitor it and fix it again if needed without removing all the staff but plastic side panel only. The length of wire should allow it.

MeganW2022

So I have been troubleshooting all morning and figured out that it is a bad wire harness. We are going on vacation in 5 days not sure if we have time to go to dealer. Local mechanics wanted 800 to replace my compressor. If you are in Venice FL do not go to Curry automotive. Do not take your Mercedes anywhere but dealership as you need Icarsoft to locate internal messages and they are not going to know that this is a normal issue with this vehicle. I was so happy when I went and stomped on front passenger carpet and that baby kicked back on. You saved my life I live in FL and it is 103 outside we would have died without this little trick until we can get to the dealership. My husband is going to take the floor panel off and see if he can tape and or clean connector will let you know how that goes. But for all of you out there suffering stomp on the front passenger floor board. It was kind of in the front middle of the mat and it works!!!!!!!!!!!

Rrichardii

Hi,
I have this exact issue, and pounding my foot has worked, but is not as effective after several times, so I want to just fix it... any other pics of the carpet removal? I though of just cutting it, but not sure exactly where the wires are located...
thanks!