There is 12volts running to the fan control board. Drop the fan and unplug the wiring . remove the cover and use electrical contact type cleaner and remove all the corrosion … that should fix it.

 

thanks.....I had to use sandpaper to clean the lugs on the motor and sanded the contacts on he board. Works great....thanks...

 

I did the same thing srtdc. It fixed my problem as well.
The real question is how did all of that moisture build up inside the coated, sealed resistor cover so I can prevent reoccurrence?

 

Great...happy for you. I'll bet the the metal nut holding the plastic squirrel cage has rust. I saw all the used ones on EBay also had the rust.
Its a design issue. The vent in the hood allows rain/snow/water in and the blower sucks it in and throws it into the board. If you open the housing on the fire wall (just 2 clips- easy)
you can see the path via the hole on the bottom.

Mine is a 2008 - 14 years old. Cleaning the contacts every 14 years isn't bad, I'll live with it. Or, you could put a sponge in the hole to absorb any water...LOL
BTW: I think the fuse for the blower is next to the battery...another stroke of genius...

 

I had this exact issue with my 2007 GL450. The blower motor would run continuously after the vehicle is shut down and locked. The wealth of information here is amazing. I was able to follow the instructions found here and successfully cleaned the blower motor circuit board, and everything now runs as it should.

Many thanks to all who share their experiences here.

 

*CONFIRMED FIX* on 2008 ML350! i had this issue happen to me in 2023, so wanted to add my story as well- as this can still happen to the w164 even in '23! here's a brief synopsis of what was happening on my w164- every once in a while the battery would randomly die overnight or after sitting for awhile, i just chalked that up to some odd anomaly that i would need to keep an eye on. however by february of 2023- i had noticed the HVAC blower motor would stay on after i turned the key off. while i did read one thread comment that said MB does this to avoid moisture build up in blower ducts, and of course theres the "REST" feature... this was clearly neither of those as the blower motor would just run constantly until the battery was dead.

thanks to this thread, i was able to diagnose and solve this very weird problem. i HATE electrical issues on cars, as they can be a nightmare to trace down.

as other users have pointed out, what ends up happening is that water from carwashes/rain/snow/etc will fall into the hood vent and drip down into the drain channel. most of it will drain as needed, but some water may get by (esp if the drain becomes plugged) and will seep into the blower motor where it will rust out the main center bearing and drip down through it and get into the bottom where the circuit board is, and short it all out- causing the fan to have a mind of its own.

i have attached a pic of my stock blower and the replacement from ebay, you can see the design revisions as well as the rusted out center bearing on the old fan on the left. especially of note, notice how the old blower on the left has HUGE openings that can easily allow water into the core of the motor. the new one is sealed up tight like an umbrella. i suspect this will be a much better design.




the new part was 100 bucks on ebay, and appears to be a revised version of the stock Siemens blower that came on the car. i suspect this revised blower motor may not have this annoying issue, but i will report back if anything comes up in the future.

the fix was not too bad, the hardest part was unplugging the old fan plugs (2 of them) in february with cold fingers on a garage floor. one plug has two clips on each side, the other one may require a small screwdriver to help you move the clip on the side. but once you get the old fan out (4 torx bolts) after dropping the panel below the glovebox (also 4 torx - same as the fan) the old unit comes right out and the new one fits perfectly - and thanks to MB desiging a pro socket, you dont need to worry about bolt alignment as they all self-locate making it much easier to work since the repair is done all by feel rather than by vision.

tested the new blower motor these last 2 weeks, in all AC and HEAT modes, AUTO and MANUAL, and everything works great. PLUS the new blower has an audible "power down" about 1-2 seconds after you shut the car off, meaning its very obvious that you HEAR a power down (and thankfully never a power UP meaning i no longer have to worry about something running all night when i dont want it to and waking up with a car that wont start.


just want to thank everyone in this wonderful thread for the great information and wisdom on the root cause of this weird electrical issue. i wanted to add my experience as well, in the event it can help some future w164 owners. this is also a great time to change out both cabin air filters as well!

huge shoutout as well to @srtdc for their knowledge and wisdom on the underlying cause!

 

I have seen this in other circuits on the GL. The system completes ground rather than supplying power. This seems to me to be a terribly vulnerable way of doing things. Rather than a component not operating when it should, it operates when it shouldn't.

 

I am dealing with the same issue I THINK with my ML320. The battery died a couple weeks ago. I recharged the battery since the battery is not BRAND NEW but new enough and in good condition. After I recharged the battery I noticed that the fan stays on even after the car is turned off. It does shut itself off...Im not sure how long after the car is turned off, but eventually it goes off. But this morning I went to get into the car to take my stepson to work and the battery was dead. No lights had been left on so I was unsure why the battery was dead again. I put the charger on the battery to start charging the battery and the second I hooked the cables onto the terminals the fan started going...turning on and off intermittently....??? Why do you think that is? Well first, should I completely disconnect battery while I'm recharging the battery? Does it matter? And second, can u show/share what did you end up doing to fix your fan issue?

 

I have a similar issue with a 2011 R350 where when the engine is off and key removed a fan blows from the vents in the third row of seats only. This will continue until the car is started next. I followed instructions from this thread, removed the blower motor from the passenger footwell. The circuit board did not appear moldy in any way. I cleaned the 4 spade contacts but these showed no sign of corrosion.

the blower continued to blow from the third row seats while I had the blower motor removed suggesting that the problem lies elsewhere. Unsurprisingly, after refitting the problem remains as before.

any suggestions please?

 

I haven’t seen anyone mention it, and I apologize if I am telling everyone something they already know.
If you run your air conditioner, before you shut the engine down, put environmental control to vent, and let it run for a couple of minutes.
It will cause more wear and tear on motor, compressor and accessory belt if you shutdown engine with air conditioning on, and or start the engine with it on.
The reason for switching to vent is for the reasons previously mentioned in the thread.
Running the vent helps to remove moisture and the problems moisture causes.

 

I have fixed 3 boards in ML’s and GL’s for the same reason. Please take a nice sharp closeup of both sides of the control board. The power is jumping over the board contacts. Also look at the power plug for the board and clean all the pins.
It is possible the board is shorted thru the power FETS also. If you are good with a multi meter you can follow the power trace and see if it is shorted thru the turn on device.

 

You probably have a secondary auxiliary pump in the rear. I do not know if anyone can confirm this but many vans have a secondary auxiliary pump and a condenser in the rear.

 

there is a rear blower motor. In the side panel on the left side (while sitting in the car facing forward) near the third row of seats. For now I have left in place but pulled two sets of electrical connections while I monitor the situation…

 

There is not a redesign on the blower motor . Make sure your plastic cover on the outside under the engine hood … where the two clips are … there is a water vent on the bottom make sure it is unclogged. My wife’s 2009 ML350 is definitely the worse out of the 5 ML’s and GL’s for getting the circuit board wet. I added a little metal filter material on top to slow any water down … saw the tip on another forum. I fixed her original motor board 3 times and finally bought a new one.

 

Its 2025 and I've just read your post. I have a 2012 SL550 (R230) which I purchased in 2011 showing the exact symptoms as you mentioned. After all of these years and 40K miles later the problems are slowing creeping through. I have a service manual that showed the (A32N1) Blower regulator which if faulty, sends a wrong voltage code to the blower that will actually start and stop the blower intermittently even with engine off. BUT, this regulator is connected to the blower motor (A32M1) so the entire blower motor needs replacement. Only GOD and MB knows why they built these parts are built this way. So....your post gives me better confidence to replace the part now.

I just repaired a major oil leak myself on my wife's 2012 ML350 Bluetec (also bought new in 2011). A leak from the filter housing and timing cover caused a virtual explosion of oil in the engine bay and caused the shredding of the serpentine belt like Big League Chewing gum. It was all in the crank, AC, alternator, water pump pulleys. It was a mess. .............it's neither here nor there, but thank you for posting your results. Much appreciated!!