venturaII

Alright - I'm pretty sure I have a vacuum leak somewhere in my ventilation system. When I'm cruising down the road and have the ventilation set to blow through the dash vents, it takes just a tiny bit of throttle (less manifold vacuum) to make the setting change to the default floor/defrost setting, and it takes a good 30 seconds for vacuum to build back up to the point where the vents correct themselves. From my experience in the past with other vehicles, this is a pretty textbook situation.

My question is: are there any areas that I ought to be checking first? Are there specific places in this particular model car that have been problematic for others? I'd rather not waste my time chasing down the entire vacuum system if there's a common place (or places) that tends to leak....

Thanks -

mbhackie

I didn't think that these cars use a vac based climate dampers. I thought they used electronic stepper motors.

venturaII

Hmmmm...if you're correct, then that makes this a strange situation. The issue I'm seeing is DEFINITELY related to engine load, and I'm assuming the corresponding vacuum fluctuation. Ideas?

mleskovar

He's correct. In fact the levers that the stepper motors actuate easily break in the early C class. Do you hear any clicking noises coming from behind the dash area when you first start the car?

venturaII

Can't say I've noticed anything "broken" sounding, but I'll listen for clicking in the dash area tomorrow morning.

If the arm is broken, wouldn't that mean that the stepper motor wouldn't be able to change which vents the air came out of? Mine seem to operate fine in that regard - they just don't stay put, at times.

mleskovar

It will cycle about 6 times and then stop if the link/motor is broken.


Yes.

venturaII

Well, no clicking sound. I can hear the diverter flaps moving as I change the dash settings.

But I still get the random change depending on how hard I'm stepping on the gas - what gives??

mleskovar

What vents are you referring to when you said...... "have the ventilation set to blow through the dash vents".

venturaII

The actual dash vents, or the ones I've always called "dash vents" - not the floor vents, not the defrost vents, but the ones that are on the face of the dash. Two in the center, plus two on either side, all controllable with the thumb wheel.

mleskovar

The thumbwheel between the two center vents controls the amount of outside/fresh air added to all vents except floor and windshield. Close it, turn up the blower and see where the air exits. Is the problem still there with the air mix closed? Also...the air recirculation automatically switches to fresh air at different intervals depending on whether the outside air is above or below 40F or if economy mode is selected. Only the Germans could make something as simple as air temperature so complex But it works grest when you learn the code.

venturaII

Ah-HAH! Now we're on to something.....I've recently been using the Economy mode for the first time, and didn't realize that the HVAC system still did stuff "on it's own".... Can you expand upon what exactly it does in this setting?



Funny - my brother-in-law drove my car to the store just the other day and when he came back, those were almost his exact words!

mleskovar

[QUOTE=venturaII;2900868]... Can you expand upon what exactly it does in this setting?..QUOTE]

You need to read the owners manual to be totally dumbfounded on all the things the Germans engineered into the car. In recirc it automatically switches to outside air if: after 30 minutes if the outside air is >40F, or after 5 minutes if the outside air is <40F, or after 5 minutes if ec is on.

JLD2k3

I have a quasi-similar issue. Didn't want to get STFF'd by starting a new thread.

My AC/Heat diverters don't divert. No matter the setting, a little comes out the floor, a little out the dash vents, and a little out the defogger. When I turn on the defogger, more comes out the defogger, but it still comes out the floor and dash a little. Mainly, this is a problem when it is really hot and I want a lot of air to come out of the dash vents, but it won't. The fan runs hard, but nothing comes out (well, a little, but not enough). Any ideas?

venturaII

I still have the same problem as before, but I've basically given up on it. The manual does describe some pretty interesting automated climate control behavior, but none of it covers what I've been experiencing.

I checked the stepper motor, and the arm is not broken, and when I manually set the controls, I can hear the diverter flap moving; I just have the issue described by JLD2k3 as well as the semi-random changing of the location of air coming out of the vents. Screwy....

dead_eye

Interesting thread. I have a similar problem.

I always keep the dash/front (the ones that blow towards you, not the windshield) vents as the only one that blows. However, if I hit a bump it would switch to blow both front a floor vents and then switch back. It hasn't really bothered me, but if there were a solution, I'd be all ears.

The second part of the problem is that when set on the off position, the ac would turn on then off again. This scared me the first time it happened because I thought the rpm blip that occurs when turning on the ac was an engine problem. Again, this really hasn't bothered me either since I usually keep the ac on all the time.

Anyway, I thought these were characteristic of an electrical problem (ie impossible to fix), but I'll keep an eye on this thread.