Hello.
I would like to know if anyone has this similar problem with the airconditioning system of the ML320 ( 1998 ) when it is turned on :

When the center A/C dial is turned from low to high/maximum A/C airflow
( counterclockwise direction ) - to increase the flow of cold air into the passenger cabin - there is a loud " clacking " noise that is heard. Only when this dial is turned clockwise - to the low A/C air flow setting and is left running for about 10 mins or so - and then turned back to the high/maximum A/C airflow setting - does the noise disappear.

Can anyone tell me how to fix this annoying noise problem?

Thank you for any help

 

It sounds like one of the vacuum activated doors behind the dash is misbehaving. Man, you have a difficult issue here. I assume the noise is coming from under the dash area, right? I eliminate the blower motor becase if it was that, the noise would not depemd on fan speed. It seems like when you demand more flow, you rattle those doors. How to fix it? I can only say, based on my experience with other cars - it's a ***** to fix!!! Is the noise from under the dash or the vents somewhere? Any hissing noises, like something is leaking somewhere? It could be very very low - park car, turn engine on, windows up, all othe noises OFF, and listen carefully for any hissing sound. Hissing would indicate a possible damaged vacuum line or a leak in the A/C system.

If you still can't find it, take the truck in for proper diagnosis.

 

yes, i have the same problem
like darkmann said it must be one of the vacuum activated valves that open and close the flaps
i personally did not have time to take a look at them yet but it,s most probably the problem

 

Bumping this thread because I've just recently noticed a strange noise coming from the heater-A/C fan. When I turn the fan speed up to medium/high speed I get this noise that sounds like an airplane propeller. It doesn not sound normal. Any ideas..... Almost sounds like something is hitting the fan. Don't really hear it when the fan is on low. I'm thinking of just sucking it up and living with it. Don't feel like shelling out any more money on this truck.

 

HI.. WHEN I START aircondition FIRST COMES COLD AIR AND THEN HOT AIR.. FANS OF RADIOTOR DONT STARTS CAN YOU TELL ME WHY??

 

Please UPDATE YOUR PROFILE IN USER CP.

 

I have just the same problem with my ML 270 cdi! I suggest that the problem is with some mechanism which is located near the a/c fan and while this mechanism is moving the fan is clacking on it. The problem with my device is dismissing after 10 to 15 secs or when I direct the air flow in different direction. Commonly said, an a/c mechanism distortion. Sorry about my language....