beekster

I have a 92 400E and when my ac is on, I hear a popping or thumping sound from the passenger side. AC works fine.

Anyone else have this and is it a precursor to a problem?

thanks

Beekster
92 MB 400E (155K miles)
07 Jeep Commander Limited 4x4

Cinnyman

is it just once when you turn it on? mine makes a thunk sound as the little valve things change the direction of where the air is coming from. Like from going from off to AC or off to VENT or Vent to AC. there is a vent flap inside that redirects the air to different places

Chinny4290

When its really cold out, mine make a popping noise as well. Though I believe that's natural to the car because nothing has malfunctioned. I think what happens is the vents close when the car is turned off so no external "dirty" air comes through the vents to dirty the cabin when parked. Then when the car turns on they open. Part of the auto A/C. Compressor on or off it does it.

I could be completeeeeeeeeeeellllyyyyyy wrong.

STLe320

that's what i was gonna say. mine does the same. maybe they all do?

Bigpete123

Mine does this too, even when I don't have the A/C on- it can be just when I'm using the fan or heater, usually around the time when I start up my car.

read something on one of the MB forums about this a few years ago... can't remember where. But I vaguely remembering there being some kind of kit you could get from MB to make it stop doing this. But it is not a problem at all.

In my case, I would call the sound more of a mix between popping and gurgling... if that makes sense.

Actually, I did a search on mercedesshop.com. scroll down to post #12:

http://www.mercedesshop.com/shopforu...=w124+gurgling

and look at post #9 in this thread:

http://www.mercedesshop.com/shopforu...=w124+gurgling

So I wouldn't worry too much about it.

beekster

thanks for the posts.

It's not the gurging, watery sound that you hear from the central vents--I have that too. This is more from the passenger side and is a constant pop every 30 to 45 seconds when the AC is on.

You are right about not worrying about it, it works. I should be glad. I need to worry about paying for a suspension update.

thanks.

RBYCC

Check the vacuum lines..vents open and close with vacuum, your valve could be cycling.