A/C compressor unit
Out Of Control!!
Joined: Apr 2019
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
VARIABLE DISPLACEMENT COMPRESSOR
The AAC module manages the clutch activity with a timer. You can set these parameters under VARIANT Coding.
Typically clutch will go off, less than 5mn after A/C getting commanded off.
Pumping is controlled by variable displacement solenoid such that compressor can be spinning and not pumping.
Last edited by CaliBenzDriver; Aug 1, 2025 at 11:59 AM.
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From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
1 - Measured pressures using pressure gauges?
2 - Used the scanner to see the electronic control valve and clutch current status?
3 - Visual of the compressor pulley? If so, would you mind posting photo of the compressor with engine running, and with engine off?
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Joined: Sep 2015
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2013 e 350
So everything in car is off, as soon as I start car, I can gear a high pitch whining noise which is a/c compressor. It never turns off, until I turn off ignition. Reason I think its a/c compressor, sometimes I don't hear whining noise, so I immediately turn a/c button, it flashes and turns off.
MBWorld Fanatic!
Joined: May 2021
Posts: 2,524
Likes: 2,041
From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
So everything in car is off, as soon as I start car, I can gear a high pitch whining noise which is a/c compressor. It never turns off, until I turn off ignition. Reason I think its a/c compressor, sometimes I don't hear whining noise, so I immediately turn a/c button, it flashes and turns off.
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
leaky A/C circuit
So everything in car is off, as soon as I start car, I can gear a high pitch whining noise which is a/c compressor. It never turns off, until I turn off ignition.
Reason I think its a/c compressor, sometimes I don't hear whining noise, so I immediately turn a/c button, it flashes and turns off.
Reason I think its a/c compressor, sometimes I don't hear whining noise, so I immediately turn a/c button, it flashes and turns off.
Once you have a scanner, live data + active faults will help your troubleshooting.
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Out Of Control!!
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W212 MY'14 M276-3.5NA @75kMi
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Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Try unplugging your A/C sensor harness connector near bottom of condenser coil, that may or may not help one bit.
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From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
I had this happen. The a/c stopped cooling and fan started running like a jet engine as is mentioned earlier. First thought the charge is low but adding more refrigerant made it worse. Then let some out and everything went back to normal.
The sensor at the bottom of the condenser makes fan go crazy fast when it sees high pressure from overcharged a/c system.
It seems Germans do not have hot days like I (we) do and their charge was too much for my weather.
Very easy to test if this is the problem.
I know- I know- Some specialists will shoot this theory down in a heartbeat...but just telling what happened to me.
My car is a 2010 E550.
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From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
So everything in car is off, as soon as I start car, I can gear a high pitch whining noise which is a/c compressor. It never turns off, until I turn off ignition. Reason I think its a/c compressor, sometimes I don't hear whining noise, so I immediately turn a/c button, it flashes and turns off.
When engine is cooled overnite, unplug the big power connector to the fan ( easy ) and start the engine and see if the whining noise still there and can it be also turned off along with AC compressor ?
Do note : AC compressor depending on your coding..... sometimes is not OFF immediately with A/C button in OFF, but has time delay.
