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HVAC Blower Fan Issue

25K views 47 replies 8 participants last post by  43sqd 
#1 ·
Let me start by saying I have seen the many threads on MB HVAC fans failing due to corrosion from water drips caused by clogged vent drains ...

We have a 2009 ML350 Base model with about 85K miles. It's had odd AC problems that we've been trying to tackle. I'm sharing some background leading to our current fan troubles in case it's helpful.

First, the compressor would stop cooling intermittently, at first for only a couple of minutes at a time but then worse. It would sometimes go days at a time working fine, and then days at a time not working at all. A local ac shop wanted to replace the whole compressor and pipes for $1300 or so, but we felt the compressor must not be the issue or it would never work.

We first tried replacing the Climate Control panel on the dash with a used one found on Ebay. Zero change -- so if it was the problem, then the replacement was defective in exactly the same way. We then replaced the AC Compressor Solenoid with a new one. Voila, this seemed to solve the problem. All was good and we enjoyed a few days of bliss.

But then, a new problem emerged: On longer drives, the blower fan would cut out after 45 minutes or so of use, especially highway use. It would often come back on if we stopped and turned the ignition off and back on. Sometimes it would come back on if we simply stopped at a red light. We thought this might be the result of overheated circuits having had a chance to cool off.

I read about the issue with corrosion on the blower motor. I took it out to try cleaning it, and while there was a bit of rust on the nut holding the fan in place, there was no corrosion visible on the circuit board or any connectors. I did some gentle cleaning with cotton swabs and isopropyl alcohol anyway. Zero change.

So, I ordered a replacement fan on Ebay. It was a new fan, but not OEM. (The original was made by Valeo, the replacement seems to have no brand markings -- BUT it seems better engineered to cope with potential rainwater leaks because the fan has a solid cone that would deflect them, and the motor housing has a drain hole.)

The new fan's air flow perhaps seemed more robust ... but the same problem persists, with it cutting out after 45-50 minutes of heavy use.

I saw one thread where a poster found that the plug on the climate control was loose, and clicking it more solidly into place solved the problem. I don't believe that's the problem, because I'm pretty certain I clicked it in place when I tried switching the panel in the beginning -- but something like this is interesting given that the fan will sometimes randomly re-engage if you stop the car. I intend to at least give it a shot.

Has anyone else experienced (and hopefully solved) this? Any ideas? Thank you in advance ...
 
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#2 ·
What comes to mind is a tired relay. I think the A/C relay is in the right rear corner of the vehicle. Next time the fan stops working you could test to see if one is too hot. While you're back there check for water in the well. On some ML's the gasket on the tail light leaks and the rear SAM is the recipient.
Skippy
 
#14 ·
Thanks, Skippy!



Thanks for the advice, Skippy. I replaced both of the black relays. I haven't driven far enough to give it a rigorous test yet, but I've come close and I believe it's working better -- not a single cut-out of the fan's operation, which is a big improvement. We even re-installed the original fan (the replacement made undesirable noises).

We have a separate problem where cool air stops when the vehicle is idling (such as at red lights), but cools like gangbusters when moving. The engine fan is running. But that's for another thread ...

I appreciate you jumping in to assist. Your advice is the first that seems to have had a positive effect (knock on wood).
 
#7 ·
As of model year 2002, ML's do not have a blower motor relay. Everything is self contained in the AAC Push Button Control Module.

A few questions:

1. when you say the A/C cuts out, do you mean the blower cuts out? Because if the blower cuts out, you will have no idea if the compressor is operating.

2. what to you mean by the A/C solenoid?

3. did you ever have a water leak?

3. when you bought the blower motor, did it come with the regulator?

4. what is your full vin#?
 

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#8 ·
Hi 43sqd, thanks for jumping in. Here are answers to your questions:

1. when you say the A/C cuts out, do you mean the blower cuts out? Because if the blower cuts out, you will have no idea if the compressor is operating.
I mean that the blower cuts out. We can still feel cold air sort of falling out of the vents, so it seems like the compressor is still cooling.

2. what to you mean by the A/C solenoid?
There is a part called the AC Compressor Solenoid Valve that connects electronics to the compressor. It is about a $40 part. I believe it operates like a switch. Installing it requires removing and replacing the refrigerant. Here is a link to what I bought: BRAND NEW AC COMPRESSOR CONTROL SOLENOID VALVE FOR MERCEDES 03-12 EV-004
I found this as a compressor solution on a thread about W211s with AC compressor issues, and saw other similar threads about VWs, Audis and BMWs.

3. did you ever have a water leak?
We bought the vehicle used just a few months ago and don't know its history in that regard, but we have not experienced a leak ourselves. The bolt holding the original blower fan onto the shaft appears rusty, but there is no other overtly obvious appearance of corrosion or water damage.

3. when you bought the blower motor, did it come with the regulator?
Yes, I believe so -- it was a complete unit. Here is a link to what I bought: New Heater A/C Blower Motor fits Mercedes W164 ML350 ML550 GL450 GL550 W251 R350 | eBay

4. what is your full vin#?
4JGBB56E59A511497
 
#10 ·
We bought the truck in November, and because it wasn't totally AC weather we're not sure if the problem was there.

We did have it scanned when the compressor was failing and the scan identified a compressor issue. We had it scanned after the solenoid was installed and all appeared good. I guess we should have it scanned again.
 
#20 ·
I've been reading about your problem because I have something similar, I think: 2009 ML320 Bluetec, went through a carwash for the first time since a 2-week-long -20C cold snap hit here in Quebec (saw lots of ice flying off from around the wipers, etc.).

While driving, the blower fan simply stopped. All lights on the control console worked as normal, simply no blower action at all. This happened within 5 minutes of leaving the carwash (still a -20C day here).

The first thing I checked was fuse #10 (10amp, from this thread) - to my surprise, there is no fuse in the slot for #10 - completely absent. Previous to this carwash outcome the blower/climate control worked flawlessly.

I've heard about clogged airbox drains causing leaks through the airbox into the blower fan area, but I'm having trouble with finding a diagram/image of where the drains are.

Does this scenario ring a bell in your troubleshooting at all? Should I book in at my Merc guy now?

Very best,
Trevor
 
#32 ·
I've been reading about your problem because I have something similar, I think: 2009 ML320 Bluetec, went through a carwash for the first time since a 2-week-long -20C cold snap hit here in Quebec (saw lots of ice flying off from around the wipers, etc.).
While driving, the blower fan simply stopped. All lights on the control console worked as normal, simply no blower action at all. This happened within 5 minutes of leaving the carwash (still a -20C day here).
The first thing I checked was fuse #10 (10amp, from this thread) - to my surprise, there is no fuse in the slot for #10 - completely absent. Previous to this carwash outcome the blower/climate control worked flawlessly.
Hello gentlemen
In order not to repeat the story, I am in the same situation as the user TrevorT.
I checked the fuse 91 ok, water drain ok and if they are still quarantined 14 days I said to unistall the engine blower.

Finally, I do not understand electronics but what I see is suspicious. I can clean the board with something or I need to change the full blow motor.....

Respectfully

Alex
Computer hardware Electronic engineering Electronics Electronic component Circuit component
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Computer hardware Electronic engineering Electronics Electronic component Circuit component
Computer hardware Motherboard Electronic component Electronic engineering Electronics
Auto part Technology Engine
 
#24 ·
The first thing to do is check to see if fuse #91 in the battery compartment is blown. If it is replace it and check if the blower works. If not...................

Remove the cover under the right side of the Inst. Panel and see if the cover is wet. You will then see the blower and the panel for the air filters which you should remove and inspect & replace if necessary.

At the blower motor connector you will see a heavy red wire. Turn the blower on and test the RED wire with a DVOM in every stage from low to high.
 

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#25 ·
Correct - blower motor does not work in any stage.

I'm going to go out shortly and check if it's changed overnight (dried? frozen?). I'll also check the rear blower as well.

We've had a snowstorm overnight here, so I may not go into the office (warm underground).

Here are some useful related links for anyone else having this trouble or similar:
W164 water damage to blower
Air intake snow screen (applicable to my climate [Quebec])



Question: From
, fuse #10 runs a blower, but there is no fuse in the fuse #10 slot. Is that significant?
 
#28 ·
Okay, I ended up taking the truck into Young Street Garage here in Ottawa.

Quick update.
After I had the truck inside during the day, I drove back home. While driving, the blower motor started to work again in all settings.
Once I got home and parked, I turned off the truck and removed the key. About 10 seconds later, the blower started by itself with no key inserted.

As the complexity of the problem grew I simply decided to take the truck to Young Street Garage in Ottawa.

It turns out that the regulator on the blower motor had failed.
They replaced the blower motor, which has the regulator integrated into it.
Just less than C$800 to fix.

Worthy of note is the shop I got to - Young Street Garage. These guys are complete pros.
Included in the cost above was the removal of both the driver and passenger seats to look for water leakage (none found).
Great shop, super polite and very experienced staff. Highly recommended!

Thanks for the guidance and instruction, 43sqn!

Case closed.
 
#33 ·
Try carefully cleaning the board with isopropyl alcohol and Q-tips first. If that does not correct the issue then you will need to look into purchasing a replacement. I found an OEM Mercedes Benz brand one on eBay.
 
#34 · (Edited)
Clean both side of the board with CRC Electric Cleaner and an old or new tooth brush.

Before you reinstall the blower, you must clear the drain ports which is causing the rain water entry.

Also replace your cabin air filters which are probably water logged too.
 

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#45 ·
Clean both side of the board with CDC Electric Cleaner and an old or new tooth brush.

Before you reinstall the blower, you must clear the drain ports which is causing the rain water entry.

Also replace your cabin air filters which are probably water logged too.
How do you remove the blower motor circuit board to clean both sides of it? My circuit board is wet and corroded. I want to clean both sides of the board but don't want to damage it when removing it. Will isopropyl alcohol work as well as CDC Electric Cleaner? Thank you.
 
#36 ·
After my experience, I learned from my mech that there is a small reed valve at the bottom of the outside air intake. This valve can become blocked, and when it is block the water will back-up to a an area where it will leak directly onto the board you've shown in your pictures. I suspect this might be what happened to yours. My board had to be replaced.
 
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