My 2000 C280 Sport has the electric climate control and when the ac or the heat is on I hear like a thumping sound comming from the center and right vents. Is this normal? or a serious problem. When it is on full blast heat or ac the thumping stops but when it is low I hear it. Also when you turn the car off should you turn off the ac or can you leave it on?

 

It might be something flapping in the ducting, if you close the vents does it go away? If it does not then I would suspect the fan. In the one car I stripped down for some ducting problems it had a centrifugal fan and these can move laterally on their bearings - might explain what you are hearing. At high rpm it settles down and no longer bounces. Would not say it is serious but it might be a sign that the fan is worn...

Which I suppose is serious from the fan's perspective - and it was a heck of a lot of fiddly work pulling it down to get at them ducts - so it may be from your perspective too!

And I never turn the A/C off! It is just a pump after all and it only pumps when it is told to - which will never occur when the engine is off.

My 2 cents worth...

Lawrence

 

Thank you for the reply. No it does not stop when I close the vents it still keeps making that thumping sound.