Vacuum tube to climate control air flow speed control


New Member
Apr 1, 2015
W124 300CE-24

I've just bought a 92 300CE-24. Once the engine is started, I hear "hee-hee" from the central console. It turns out coming from the air flow speed switch - the left dial in the following picture:

I get it out

As you can see there are 2 nozzles that connect to 1 vacuum tube in green and 1 vacuum in red. The green one is with negative pressure.

On the other end of the nozzle (behind the piece of metal, there are two hair-thick hole getting through to the nozzle. When engine starts, air is sucked through the hair-thick hole to the green tube and causes the loud "vee-vee-vee"

Just wonder any idea if that "vee-vee-vee" is normal?

Any what is the purpose of connecting the air flow switch to the vacuum system?

PS all pictures borrowed

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