ive been having this problem with my 01 clk 320....basically the blower will work intermitently. sometimes its never an issue, sometimes it is. it will work, then shut off for a few mins and come back on. sometimes it will only do it once or twice, other times the blower barely comes on at all. i has pulled the ac codes and i was told that the high side ac sensor was bad. however, now that the weather has cooled down and ive needed to use the heat for the defogger, ive noticed that its the same story with the heat, it works intermitantly. im leaning towards it not being the high side sensor since its the same story with the heat. ive also tried hitting the EC button, which is supposed to turn off the ac compressor and its the same thing. im begining to think its possibly the blower motor resistor, but before i buy a new one id like some opinions. is it possible that the ac high side sensor would cause this problem?

 

Pressure sensor shouldn't have anything to do with the blower speed. All its going to do is shut the compressor off. The pressure sensor fault may be due to low freon level. The blower motor regulator is what controls the blower fan speed. I would go with the regulator first, and see if the blower motor itself is faulty as well. I believe there is an updated motor/regulator combo now, but not 100% sure.

 

https://mbworld.org/forums/e-class-w...-diy-here.html

 

I had the exact same issue and it turned out to be the resistor thats connected on to the fan motor. I would check Ebay and see if you can find the fan cheap because they sometimes keep the resistor connected to the fan. Then you can sell the fan motor by itself and make most of your oney back. It is really simple to get to the fan as well through the passenger side dash.

Greg

 

well im kinda doubting low freon since when it does blow, its ICE COLD. i guess its possible and i could throw gauges on it to see where its at. adjusting the fan speed isnt an issue when the blower is working. i can control it no problem and all levels work....its just that sometimes the blower shuts off completely.

 

my friend suggested that it might also be the blower motor relay. what do you guys think?

 

I can almost guarantee you that it is not the relay.You can spend the money and buy a new relay but your problem is the resistor thats connected to the fan motor. These go out on our cars with the exact same symptoms that you have now.

 

Ok guys - I have searched but no one seems to experience what I am: my w208 clk. Sometimes, The fan level literally decreases (or sounds like it does) when I speed up and hit a certain RPM, then once I start coasting at my speed and the RPM reduces, the fan speed increases. (although it doesn't indicate speed changing on the climate control)

Do these vehicles have some kind of speed dependent climate control? Or is this an issue?

I don't have the issues others reported - when I select a fan speed, The fan/blower increases or decreases as it's supposed to. This phenomenon only happens when speeding up or down...More RPM related.

My battery is brand new by the way.

 

No, it's an issue.

PS: The only speed-dependant thing is the increased air flow as you speed up, caused by more air getting in (irrelevant to blower motor rpm). Activate air recirculation to get around that.

 

Sounds like the typical motor resitor to me ! the one with the spikes on. Also check the brushes in the motor are not worn too far.

 

@Johnnr
I had the same problem. In my case it was the blower motor resistor. An OE Behr cost about $100 when I bought mine and it takes about 20 minutes to install.

 

Thanks Marcus!
I ordered one from Autohaus (the Behr OEM).
I was speaking to a Benz mechanic today on another matter and mentioned I'd be replacing the regulator. He said it would be good to change the blower itself while I'm at it because sometimes one can negatively impact the other.

I haven't read much on these forums where folks choose to replace both. Seems like a replacement of just the regulator would be ok. For less than 100 bucks, its a good start.

Thoughts?

 

I replaced both at the same time in December as the resistor failed and no heat. Considering the noise from the old motor total cost was under $175(Amazon) and it was a pretty simple job. If the motor was quiet I would have changed only the resistor.

 

I only changed the regulator. I suppose you could swap the regulator and do the motor if it doesn't work like new.

 

I found that a clogged cabin filter with an aged blower fan will take these out fast.

I am going for a 2nd resistor or porky pine module along with a new blower motor.

Found cabin filter plugged solid with pollen and leaves after sitting for a couple months.
Once the porky pine resistor module overheats its a gonner. At least they are reasonable and easily replaced.

 

Unfortunately the regulator didn't solve my issue with the fan/blower speed decreasing and increasing with vehicle acceleration and/or engine power consumption. (foot on pedal, vehicle speeding up...Blower speed decreases. Foot off pedal, it increases back to normal)

Note I didn't use the wires that came with the new one... I re used the existing ones. Could this be an issue?

Note when revving the engine in parked mode, everything works fine.

I don't see how this can be the blower motor... It is quiet and seems to work just fine! However, electronics can be unpredictable I guess.

All symptoms totally are indicative of the regulator!

And I'm not sure of what other things can impact this. No other electronics or accessories in the vehicle are impacted when I accelerate or take my foot off the pedal... Only the blower speed. I know there is some speed dependency built in to the blower, but this seems excessive so I don't believe it's normal operation and I think it occurs not really with speed - but acceleration and letting my foot of the gas. Hard to explain.

Anyhow, since a blower motor from autohausaz isn't too expensive (and maybe I can return it?) I will try that. Maybe there is an issue with the connection or something? ... Taking the advice of my mechanic and replacing both after all.

1) What do you guys think of the overall situation?
2) while I wait for the new blower, do you think it's ok to use the climate control with the new regular and the 'potentially' failing vlower? (Will it somehow mess up the new regulator in the next two days or so?)

 

Theres plenty on ebay second hand, I would consider replacing both the motor and regulator, did you you check the brushes as I mentioned?

 

Yep, the blower looks and operates just fine.

After more research, i believe I've identified a potential vacuum leak... And this having been the likely issue all along. (I may not have sensed the true symptoms... Thought the blower speed was reducing and resuming back to normal after letting up on the gas but what is really happening is as I accelerate, the air distribution changes from vents or floor or where ever, to, I think, the defroster vents, then resumes back as I let foot off the pedal. I misidentified the symptoms because it genuinely sounded as though the blower speed (air output) decreased and increased all together. However, it may not be... I think it's just being diverted to the defroster vents.

As such, I canceled my order for a new blower and will see if I can find the leak and do something about it. If not, I think it's an issue I can live with.

Since Autohaus doesn't accept returns on electronic items, I'll stick with the new regulator and try and sell it (or the old one)

 

I wonder if your diagnosis of the vaccum leak was corect? Did you fix it?
For me I had much the same symptoms but also seemed to come on when driving over a speed bump so a loose connection, bad solder point etc seems to be invovled too. Currently the blower packed in completely.My secondary syntomps were no air from the center dash vents which are vaccum controlled I believe so I would concur with your assessment of a vacuum issue. As my vacuum system, door locks, head rests is not working but the vaccuum pump is running my issue is at least partially vaccuum related. thank you in advance for any replies, assessments. Johannes

 

I did have it looked at: it was indeed the vacuum - one of the vent bellows has a small leak. The below is behind the dashboard.

Since then, I haven’t done anything - the issue is the same and it really is not much of an issue. The re directing of the air to the defroster vents only lasts a little while
when accelerating, then it’s back to normal.

So all in all, im not losing air - it’s just coming out of defroster vents for a short period.

FYI - To repair bellows is a big job, with a high likelihood that when removing a 20 year old dash, it may crack.

And, if you’re gonna have the dash out, may as well replace all the bellows. (Wouldn’t want to take it all apart again if another bellow goes)

So, as you see, this becomes a cost and time probhibitive project. Just not sensible for a minor issue. (On my car that is, not sure what’s up w yours)

 

Thank you for the quick reply, johnnr.
Yeah, I wouldn't take out the dash either.
Will see what my issue turns out to be.

 

Hey Johnnr,

Ran across your post on air flow dropping off. I have the same problem, air flow stops when accelerating from a stop, once I stop accelerating air flow returns with a blast and remains so. This only occurs when outside temp is over 90 and engine is at operating temp. AC runs cold and everything else works. I believe it is a vacuum
problem as manifold vacuum drops when accelerating. So far I have not been able to remove blower cover and see whats connected to blower. There are 2 yelllow tabs holding blower motor cover on and I have not been able to remove these to access motor. When air flow stops its not being redirected to floor or defroster vents.
I hate to go to shop for this because everytime I do its a minimum $800 repair. I live in the desert and use AC 9-10 months of the year.

If you have any suggestions they would be much appreciated.

 

mkoons........from what you describe, it does sound like a vacuum issue.

There is a vacuum reservoir to that should ample vacuum, under all driving conditions, including the HVAC system.

I previously posted some diagrams of the HVAC system here , which could help troubleshoot where leaks could develop.

Additionally, running the 'Individual Flap Test' (via A/C Pushbutton Control Module [N22]), might provide some clues.