Hello, I recently noticed there is intermittent short buzzing noise from the AC control unit "lower deck" from my C300 4Matic. It started 2 months ago "the time when i noticed it", however, I am not sure if it was there since day 1, perchance music from the sound system camouflage the issue...... Anyhow, I brought it in to MB since it should be under warranty and it came back No Fault Found. Based on educated guess, MB replaced the unit anyway (at least they claimed they did and no service paper work available at the time when i picked up my car) and since then, it's been quiet until now "four days later", i started to hear the intermittent short buzzing noise again. I am wondering is this noise a standard thing from the unit or, MB just fake they replaced it or something else ? Any suggestions ? Thanks

 

If you don't trust that the dealer actually replaced the unit you have a major problem right there. The best way is to ask the dealer to let you listen to another couple of 09 C's and see if they make same noise. It is pretty possible that it is a normal noise, I will see if I can hear anything similar on a like model.

 

I do trust MB service, in my 25 yrs car ownership history, i would rank MB service one of the best in the community, i just can't figure out why....

Thank you for trying to duplicate similar problems on a like model and the buzzing noise is very short and it lasts only a second or two at most. It is also not a loud buzz either but for sure you will notice it if the radio is off and no one is chatting inside the vehicle.

 

I didn't hear any abnormal noises from the ac control unit that I checked today, but that doesn't help much. If you think it is not a normal noise, or it is overly annoying to you I would take it back to the dealer and have them make a decision with you as to weather it is normal or not.