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Hissing noise/no air from dash vents

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C-Class (W203) 2001-2007, C160, C180, C200, C220, C230, C240, C270, C280, C300, C320, C230K, C350, Coupe

Hissing noise/no air from dash vents

 
Old 07-09-2019, 02:29 PM
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2002 Mercedes c240
Thumbs down Hissing noise/no air from dash vents

Hello everyone,

Since the stickied thread on this subject has seen one post over the last two years, I'm making a new one. Maybe the mods can sticky this thread and give the subject new life.

Anyway, I have a malfunctioning vent system on my 2002 C240. I can not get air from the dash vents (the ones directly facing the driver/passenger seats). This inoperable state is accompanied by a hissing noise for several seconds when trying to change the direction of the airflow. I understand the sound can be coming from the vacuum lines that control the directional vanes. My question is: where are these lines located and what is the best way to get at them for inspection/repair? Do I need to pull the whole dash off in order to access the lines effectively? The previous owner of the vehicle blamed one of the stepper motors for the issue, but I'm starting with the simple/inexpensive things first.

Any input on this subject is appreciated.

Thank you
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Old 07-12-2019, 06:20 AM
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2003 C230K Coupe Orion Blue
A W203 doesn't have vacuum lines. The HVAC dampers are all controlled by electronic stepper motors. Your C240 has 6 of them spread throughout the interior under the dash, behind the instrument cluster, radio, and glove box.

Not sure why you had to start a new thread, as the information would be unchanged from before. You either need to re-synchronize the HVAC system, or replace any motors that died (doesn't look like the case in your situation). The stickied thread probably has what you're looking for. What you're describing is a very common W203 (and whichever other models use the same stepper motors) problem.

With that said, these stepper motors are known to fail when the gears wear out and teeth break off. It's always a fun time ripping out the entire dash area. One of the most difficult (time consuming) repairs for the W203. I still have nightmares over this.

Last edited by slammer111; 07-12-2019 at 06:23 AM.
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