occasional Squeal
 

HAve a 2000 E320w 147.000 miles. after the car warms up and occasionaly at any time with AC on, mostly at a stop or slight acceleration, A little squeal comes from the middle to passenger side of the dash for about a second then goes away, (sounds as if you tore a small hole in a balloon and stretched it out and it squeals) takes spells of doing it frequently, then goes away for no reason. Ive scanned all systems with no fault and checked in car filter for proper operation... any ideas???

A split in one of the a/c vacuum diaphragms?

Try selecting different a/c button positions & see if any position stops the noise.

Like try the EC setting. If that removes the noise then the fresh air diaphragm is the most likely culprit.

thank you! very helpful, found the control valve assembly to be leaking with smoke machine!!!!