kavadarci

So here is something interesting i've noticed on my few months old W211.
When the cabin a/c or heating is not on, everything sounds normal.
The minute i turn it on and weather the a/c compressor is on or not i notice whining sound from what i can describe the area behind the steering wheel.
It changes with the rpms change. It is very faint but i hear it.
I thought it was the transmission but again if the fan is not on it's not there.
i removed the fan from under the glove compartment to clean it and looks like new and there it normal fan noise when on.
I then looked at the air circulation fan in the upper console and i can hear it running as a normal small fan, no whining.
then i tried hear the fan on the right hand side of the steering wheel opening and it doesn't sound like it's coming from there.

Is there another fan somewhere or inside the engine bay?
has anyone experienced this?

It's almost impossible to capture it on audio so you have to take my word for it.

Appreciate the feedback.

juanmor40

If I recall correctly, there should be a fan at the back of the COMAND unit, as well as the motor for the CD/DVD player

kavadarci

Correct but the noise was there even with the head unit out recently for some sirius connection.
It's more inside the dash OR leading into the engine bay.

juanmor40

Perhaps looking at the parts diagram for the AC system, and understanding the location of the moving parts

Sedan: http://mbepc.net/1/fg/e/65h/211056#gsc.tab=0
Wagon: http://mbepc.net/1/fg/e/65j/211256/0/83/#gsc.tab=0

tjts1

It's it's not the fans. You're hearing the AC compressor through the lines. That's why the pitch changes with engine RPM, not fan speed. Turn the AC off but keep the fan on, wait about 3 minutes until the AC compressor is completely (it doesn't switch off instantly). Behold no more noise. Every time you start the engine even if the AC is switched off your AC compressor is running that's why you're hearing. Wait a few minutes with the AC switched off and the noise goes away. If you hit the big O button in the center of the climate control unit the noise goes away instantly because the AC compressor switches off instantly along with the fan. My 04 does it too.

kavadarci

ok
i will test this later.
what is the big O in the Center console? Is that off?

and if this is the case with the a/c compressor what is the fix? New compressor?

juanmor40

Off/On for the compressor. It is both. Basically, it does the opposite of what it currently is.

I would not jump on a new compressor so quick.
1 - Check codes for AC system
2 - Measure pressure on both sides,: high and low, using the appropriate procedure (discussed in other threads in the forum). Are they within the specifications?
3 - Perhaps worth reading https://www.mercedesmedic.com/diagno...mercedes-benz/

kavadarci

Ok, checked for codes and all is clear.
Your logic holds water on being the a/c compressor.
I will use statoscope to confirm.
So, looks like might be the a/c bearings (not the clutch) and wondering if i should tackle that next.

tjts1

One person in a previous thread mentioned it might be too little refrigerant in the system. To be honest I've never checked my pressure. The AC blows ice cold in mine.