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A/C Noise 2006 R350

7K views 9 replies 7 participants last post by  leebenny74 
#1 ·
Our A/C is pumping cold air, but when you turn it on there's a strong revving noise under the hood. It's like the engine is revving at very high RPM, but it's not the engine. The noise stops when we turn off the A/C.

We leave soon for a long trip (in this vehicle) so need to address quickly!

Thanks.

JV
 
#2 ·
I notice the same thing since my car was about 30,000 miles (I bought it as CPO at about 25000 miles in winter time). Brought it in to the dealer couple times; said it's normal. Didn't trust the dealer so brought it to another dealer; also said it's normal. Now about 50,000 miles, noise seems to be lower, but still can hear the humming noise when a/c is on.
 
#3 ·
Does it sound more like a loud whining noise? Does it sound like a fan noise?? when the a/c is on, especially when its humid out, the electric fan runs close to max capacity so your a/c system functions properly. this is normal, and it sounds like this is the issue you are talking about due to the fact that is stops when the a/c is turned off
 
#4 · (Edited)
Perhaps that is what the occasional noise in my R320 is, with the air con on. However, at low vehicle speeds, the noise level rises and falls with engine speed as the auto box changes gears. I can make it come and go by turning the air con on & off. Pretty weird!

Are we talking about the ventilation fan or the radiator cooling fan here? Certainly, the vent fan isn't running fast when I hear it..
 
#6 ·
On the half dozen R500's I've driven they all have a light but pronounced humming at idle which goes away when the A/C is turned off. The revving is the fans which have their own very distinctive noise because of the air movement. Just an fyi....2 of these vehicles had steering pump/rack problems.
 
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