RJC

Why does my AC compressor emit a rather loud buzzing noise? The MB dealer has replaced the compressor once already but the noise remains; is there a valve of sorts that controls the compressor's pressure, as I've been told that the noise I may be hearing could be the compressor overcharging or charging too often?

Thanks


2004 CLK 500

RJC

Can any of the MB Tech's help here...

Thanks

516mbtek

I have never heard of this condition. The buzzing is likly from the p/s pump---located right above the compressor. These a/c comps do not have a clutch like a standard compressor--variable displacement is the type. They really dont fail often.

RJC

Thanks for the reply. It's not the power steering pump as that's been checked by MB already.

The noise only occurs when the AC is turned on, the AC works very well but the compressor emits a very loud buzzing sound (similar to what a neon sign sounds like) for most of the time the AC is on; it gets especially loud right when turning the AC off then the sound goes away completely, about 10 seconds later.

What part(s)could be causing the compressor to overcharge/over pressurize?

Thoughts are most welcome as this has been occuring since the car was brand new.

liz

I have a deep whing sound in my a/c. whenever it's on and the car is accellerating (especially 1st to 2nd to third) it whines. The sound is similar to a whining transmission. Nobody has been able to rectify this.

516mbtek

RJC I have done some research and have found nothing. I checked dtb's. I checked another clk and it sounded o.k....a slight whine-buzz is heard, mainly when cold, and is said to be operating as designed. I would say....wait till it fails...if it ever does. If the car came new...having this noise and having no repairs or bodywork..probably nothing is wrong with it.

516mbtek

Whats the year and model?

RJC

Thanks for looking into this...the AC works great but the buzzing sound is just very loud, annoying and occurs aout 95% of the time. What controls the pressure of the compressor as I think it may be over pressurizing?

Thanks

516mbtek

The pressure is controlled by the control valve (solenoid) on the side of the compressor. The control valve is given a pwm signal according to various inputs to the a/c control panel...inputs:all temp sensors, humidity, sun, evap temp, and engine coolant temps. hope this helps

RJC

Thank you. Is the control valve a permanent part of the compressor or is it a detachable part that may not have been changed when MB switched out my compressor? If the control valve is a permanent part of the compressor and it was therefore changed with the replacement compressor, what else should I be looking for causing my compressor to pressurize too much/often?

Thanks again 516 mbtek!

ScottCLS55

My S500 does it also, so did my last one. It sounds like the bearings or valves in the compressor. The air always works fine.. It is annoying, and very noticable when you drive away from a drive through window with they air on. I figured that the A/c compressor replacement would cure it. Did you get a new ac compressor or a Remanufactured one??

Scott

RJC

Brand new compressor under warranty from MB, it makes the exact same noise so it has to be something causing the compressor to over-pressurize . I also heard a W203 make the exact same noise at a 7-11, but I never had this on any otherMB's I've owned.

516mbtek

The pressure control valve comes with the compressor. I would suspect incorrect version coding in the aac control unit or a faulty input signal. But, it is always likley that this may be a characteristic of this hvac system...and...well you have heard it before...normal operation for your climate//elevation//temp etc. etc.

RJC

Again thanks for the help. The W203 that made same noise was the only other MB that I've ever heard making this dreaded sound. I will ask my tech at the dealership to look into the items you mentioned. I also owned a 2003 CLK500 that had a very quiet and normal sounding AC. If you happen to come across any other info/ideas please let me know.

We appreciate having a resource like you @ this forum.

516mbtek

You bet. Be sure to let me know what he finds in case I run into a similar problem like this in the workshop

liz

my car is an 02 e320 4matic with a new compressor and radiator (accident). any help would be greatly appreciated. the noise is loud and constant. especially when the car has been running for 10 or more mins. my star mark warr. runs out in oct 06. we've been hoping the system would fail enough to be replaced as they simply cannot alleviate the problem. i try to keep the system off and long as humanly possible as it is so annoying. the kia cheapo rental had a quieter system. sorry for complaining, i am just very frustrated. again thanks for any info.

516mbtek

If the noise is that bad why cant they fix it? Who did the work... a bodyshop, dealer, independent? What are they telling you? That they cannot duplicate it..or its normal..or what? I recomend that u request to test drive with the tech and tell them what u want fixed. If the noise occurs ONLY with the a/c on, and it is coming from the engine compartment, and it is totally excessive..and they put a new compressor (complete unit I assume) they its likely...they forgot to put oil in the new compressor. Or the new compressor has failed for other reasons. If the noise occurs all the time, wheather a/c on or off...then it sounds like a p/s pump. Check the fluid w/ engine running...the p/s pump reservoir cap (black, drivers side) has a little dipstick. Oct 06 is a long way away...

liz

2 different mb dealerships worked on the car-many times. 1 said it was normal. the other replaced some pulley item. the problem occurs only when a/c is on. i did have the harmonic balancer replaced previously, and considered the issue possibly related (drier/ reciever or damper(something like that(?)- heard that somewhere on this website. i did drive the car with the sa to show him the issue, he found it to be exceesive. techs said nothing registered on the comp. relevent to the noise. however, the system is constantly 1/2 lbs low (3x in one season). dye was put into the system but no leak found (according to sa). i must bring the car back in again as there is ticking sound on drivers side of engine and the belt makes loud noise. I was just hoping to have a clue as to what this could possibly be. thanks again for helping.

liz

sorry -ticking on passenger side

516mbtek

Wait to see what happens w/ the belt noise issue..this may be related to your original concern w/ the a/c....??

rrpnow

i have the same A/C noise... i drive 06 c230... and its a bit annoying..

RJC

Have you had it checked out?

RJC

I see there is a TSB (P83 55 65 Dec 02) for the 2002-2004 C class that ,mentions the AC compressor cycles too frequently; I wonder if this issue could be giving some of our problems?