My 2003 Mercedes C230 Coupe has a knocking sound coming from the dash when started. After about 30 seconds it stops. My A/C also is blowing hot air... could these two issues be related? If so what is the problem? If not what is this loud, consistent knocking that I hear?

It happens every time my car is started.

Thanks!

 

Knock-knock? Is it more of a knocking or clicking sound? When did all this first started appearing when you start the car? IE Did you fix or change anything on the car? Did you recently change the car battery?
Is AUTO function on?

Try resynching your HVAC system:
- press both front-window defroster and re-circulation buttons together for 10 seconds
- when in resynch mode lights on both of the above buttons should flash on and off alternating between each other (let go of buttons)
- if your HVAC resynch turns itself off in about a couple of minutes then your HVAC system is good - if not, it won't turn itself off - report results

 

That's weird its only when the car is started. You'll need to isolate the noise, what part of the dash is it coming from?

 

Thanks for the quick reply!

It is a repetitive knock, knock, knock, knock...
It has been doing this for a month or two now but I'm just now getting around to it. There was no maintenance preformed or I didn't mess with anything. The AUTO function is not on.

I tried the resynch and after about 5-10 minutes the HVAC system did not resynch so I shut the car off. When I went to restart the car it ran rough for a few seconds after start...

Recommendations? I'm guessing this isn't good.

Thanks again!

 

Not sure what part of the dash it is coming from... maybe the center???

 

After doing some research it sounds like it might be the stepper motor... does anyone have any idea of how much that will cost to repair?

Also could this make my A/C blow warm air? Could it cause a leak?

Thanks!

 

From the centre would be a good indication its a stepper motor, many are located near the centre. It depends on which stepper motor - the dealer can read codes to tell you which one is sticking.

Some are easy to access, some require a lot of effort. If you're unlucky that its the stepper motor that controls air blending (ie changing from heat to cool) then if I remember correctly its a PITA to access.

Stepper motors will not cause a leak, and if your AC was low on pressure the AC off/EC Rest light on the climate control would be on.

 

The heat gets hot, but the A/C puts out warm air... after getting it charged it put out cold air for a while... so my best guess would be that it is not the stepper motor that controls air blending, but also that I have a leak somewhere. Just my guess...

 

I think it's more of a click-click,... well, a loud click-click (you say po-ta-toe, I say po-tah-toe) that you hear every 5 seconds when you first start the car,....

Since your HVAC didn't turn itself off within a minute for so of the resynch,.... there's something wrong / broken,... likely a plastic linkage arm,.... and that click-click (knock-knock) sound is actually a small stepper motor that's likely not broken but is connected to a broken plastic linkage arm. R emember, the vast majority of the time, its NOT the stepper motor that's broken and need to be replaced,... it's usually a plastic linkage arm that's broken, cracked or stuck.

Forget about going to the Mercedes-Benz Stealership to get the code read to figure out which part of your HVAC isn't working! You have hands don't you? And you can feel which vent the air is coming out from,... right? Then why would you pay the Mercedes_Benz Stealership an hour labour to diagnose this for you.

Next step,... start playing with your HVAC system,... turn on and alternate between fan, AC, heater,... alternate the air flow through foot well vent, dash vent, defrost vent, etc,... and feel where the air is actually coming out,.... IE - even though you're testing dash vent, give it a second or so and feel for air all the other vents as well,.... one of the vents is either stuck open or closed.

This is a common and most probable breakage,.... My bet is your foot well vent plastic linkage arm broke,... likely cracked,... your foot well vent will either always be open or always closed (likely always open) regardless of which vent you choose. The plastic linkage arm for foot well vent is Mercedes-Benz part# A203-830-00-33 (HVAC Control Lever Kit For Left/Right Footwell Flap Levers - $20 in US MB-dealership and $30 at Canadian MB-Stealerships),... that was the good news,.... the bad news, you'll need about 6 hours to take apart the dash to change this part,... Thus, if you take it to the Mercedes-Benz Stealership to get it done, it'll likely be about $1,000 to fix and most will be for their labour to replace a $20 part. If you really don't care about the foot vent (if its stuck open it'll actually mean less air to the other vents, eventually if you're lucky the plastic linkage arm will just break off and the click-click noise will be eliminated),.... my suggestion, take the dash apart and do it yourself,... oh, and change both left and right at the same time, it's upgraded to redesigned stronger parts,.... and that HVAC Control Lever Kit contains both.

Anyways,.... start reading,.... very good DIY here from Racin_Fool with photos from LiveNiceGuy and commentary from Mleskovar
https://mbworld.org/forums/c-class-w...g-hissing.html

 

I will not take it to the stealership, but if it means killing 6 hours or in my case probably 12 hours I will take it somewhere besides my driveway to be fixed.

Thanks for all the info! You guys rock!

 

6 hours seems to be the amount of time most people on this forum needs to fix this issue the first time. Most think they can do it in 3-4 hours the second time,... the Mercedes-Benz Stealership could probably do it in 1-2 hours,... but they will charge you for 6 hours of labour,... because they can!

Bottom-line, its more enjoyable to do it yourself,... and you'll also learn more about your car. BTW, if you're thinking about upgrading your radio or something,... now would be a good time since you'll have the dash apart anyways.

 

A knock coming from the front of the car when it's cold would worry me a lot unless I was SURE it was NOT coming from the engine. From your initial description, it sounded like it could be getting ready to throw a rod. I pray it really is an A/C or some "little" thing instead!

 

"knock" is definitely a bad term to use. People unfamiliar with engines tend not to know this since engine knock isn't very common anymore. Hopefully it is more of a "click" than a "knock".

 

I have the same car , the same problem.
Click every 5 seconds, doing this 7 times, then it stops. It happens every time i start the car.
Can you tell me if/how your issue has been fixed?

Thank you

 

start reading,.... very good DIY here from Racin_Fool with photos from LiveNiceGuy and commentary from Mleskovar Everything is here,.... step by step with photos,.... doesn't get any more detailed than that!
Noisy Air Conditioner ?? Stepper Motor Replacement / Clicking & Hissing

 

This is a recall for the c240 , c230 has the same problem .

http://repairpal.com/broken-stepper-motor-actuating-arm-may-cause-clicking-noise-from-behind-dash-545

 

Knocking noise coming from dash board when I start car and continues for a little while then eventually stops.

 

Recall? I don't see any recall for that. Sure would be nice, I have hot air blowing the floor no matter what setting.

 

No recall. Only warranty repairs at the time.

See link. HVAC stepper motor replacement