C300Sport

I washed my car Sun and noticed an intermittant sound every 5 or 10 seconds while I was washing the front wheels. Almost like an electric motor engaging and disengaging. The car was off and had been overnight but I was wondering if this was the brake drying function?? It came from the front end close to the wheels and I only noticed it while I was rinsing the front end and the wheels?

white_glass_top

i have heard it several times myself, thought it might be the TPMS??? dont no, I can ask next time im at dealer

angeloxnet

i also know about this sound, same goes for a friend's C63.
I believe its some kind of FAN (possible for the Command) it runs for a while even after the car is off and key is out

joshg1001

thats so weird. it cant be the brake drying feature cause thats when the brakes are actually being used.

but thats interesting you mention this, because i was sitting in my car (off) and i noticed that just wen you pull the key out, the command center continues to hum for a while. weird.

RLE

My W203 did the same thing. It's the AC system, probably refrigerant flowing slowly from the high side to the low pressure side. Entirely normal.

What about your cell phone? Mine beeps loudly when I come in range(or leave it) when walking near the car in the house. Even when the car is off.

nguyenmd350slk

It's halloween....!

MB Fanatic

Either the freon moving or it could be the air injection pump. all are normal to a certain extent.

RLE

Well, not to put to fine a point on it, but MBs have not used freon for 15 years and the pump is an electric motor which can only operate when the key is on.

It's R134A.

MB Fanatic

yea yeah its R134A. it could be the pump since on the e63 there was always this noise and the dealer isolated it to the AIP so thats why I mention that.

whkento

Maybe she was just enjoying the attention!

JimPap

......or enjoying a bubble bath.

PhaseNine

......or a hand job wakka wakka

Star & Laurel

The humming you hear inside the car is the cooling fan for the command / radio. it runs for a little while afterwards to keep it cool.

darstar

My wife's C300 makes a strange beep sound every 5 or so minutes after I wash the car.

C300Sport

The car had been turned off for almost 24 hours so it wouldn't have been any type of cooling fans, etc. It was sound similar to an electric motor or solenoid, pretty faint but distinct on and off sound that would last only about 1/2 to 1 second each time. Really sounded like it came from the brakes but I am not sure. It only did it when the wheel area was wet...

Hazemonster

C300..you are not crazy. I heard the same thing about 3 weeks ago. It is NOT anything to do with a fan for COMAND. I was leaving the house at 5:45 AM and opened the garage door. I passed the car (which had been sitting parked inside the garage) and put something in my mailbox and on the way back I heard what can only be described as a cross between a short squeal and a hiss coming from the car. I was like, "WTF?". I bent down closer to the hood and heard the noise again about 30 seconds later. This time I determined that it was coming from BEHIND the brake rotor on the left front wheel. I put my head close to the wheel and the car made the noise again about 30 seconds after that. I have NO IDEA what it was...but got in and drove to work. I stopped by the dealer on the way home, but they couldn't find anything wrong with the car. The tires still had all the proper air...and nothing has become of it since. Each day when I go out to my car, I listen for the noise...but it has never happened since.

C300Sport

lol...yeah there is a lot more humming, whirring and buzzing in the C Class than any other car I have owned, but so far most are identifiable and are the result of good technology...hopefully this is just another one of those.

bakedNYC

Same as Hazemonster describes. Even when the car has been cool for some time I hear the same hissing/beep coming from the left front side of the engine compartment. It persists for about 30 seconds with a few seconds between each hiss/beep, sometimes cycles multiple times. I thought at first it was coming from behind the left front tire, but when I pop the hood and remove the engine cover it seems to be coming from somewhere closer to the block. I also took it to the MB dealer and they could not reproduce.

RLE

Don't you like the answer which was posted earlier??

It's refrigerant expanding through the system and can be heard randomly even a day after shutdown. It is entirely normal.

Moto_Guzzi

I was told it is a function to keep the air circulating after you left the car, for your benefit when you return, not cooling other eqpt..It's explained somewhere in the manual apparently.

Diesel Benz

Did it sound like the same as when you stroke a cat.

Diesel Benz

I almost always talk about freon when I know it is R134 or something similar, and those I talk to understand it is R134.

But where did you get the idea that the W204 compressor was electric motor driven? All I've seen have been belt driven. Anyway, even an electric motor driven AC would have pressure stored in that can take quite a while to even out.

C300Sport

That is a feature on some MBs but it's not available on the C Class...at least not in the States. I am sure the S Class has it but not sure about other models.

RLE

Nobody anywhere ever posted anything about the compressor. The person speculated about the air pump which is part of the emission system which I said cannot operate unless the engine is running.

RLE

Whoever told you that is not well informed on W204 features because the REST function, a feature of the W203 and others, was one of the features from the past that we lost in the W204. It was called REST and was activated by a button on the heater panel. When running, the auxiliary water pump (keeping water flowing since the engine's water pump was not turning) and the heater fan motor, running on low speed, kept the cabin warm or in summer just flowed air to keep it cool-ish. It would run for a timed 30 minutes or until either water temp dropped below a certain limit or battery voltage dropped to a certain level. When in heating mode, the duo-valve (regulates water flow into the heater core and used to be called the monovalve) could be heard pulsing. Clunk...clunk...clunk.

I used this all the time in my C320, winter and summer, and miss it nearly as much as mirror tiltdown.

So, since we don't have it, it's not in the manual.