When I turn the temperature dial past a certain point (going cooler), clicking noises come from behind the dash area in my 1998 ML320. This happens when running or when the key is just turned prior to starting.

What is causing the noise and how do I fix it?

Thanks

The heating/cooling system has a "blend air" system that mixes heat with fresh air to achieve the requested temp. There is a control motor that moves that blend air door...sounds like that blend air motor could be the noise..Does it change or go away if you change the HEAT control thru its range?

REQUIRES complete dash removal to replace.

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Yes, the noise goes away once I move the heat control from the coolest (6 O'clock position) to ythe 9 O'clock positon. Where is the motor located? How do you remove the dash?

Thanks for your help,

Stuart

That is a 6-7 hour ordeal at dealer...not a typical DIYer..

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Is there any way I can disconnet the power (fuse?) to the control motor to stop the clicking? I do not really adjust the temp living in California.

Thanks,

Removing any fuse will shut the complete system down, you could have the out put to the blend door motor disconnected at the control unit...

You might have to install a heater shut-off valve..better off repairing the system.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I am trying to figure out a way to stop the noise without taking the dash off and spending a lot of money. Any suggestions??

Thanks

If you remove the glove box, you can get a close view of the actuator motor. It sits on top of the whole A/C housing thing, left of the airbag. If you have a small hand, you can fiddle with the A/C temperature dial and hold the actuator to verify if that's your problem.

With mine you can see if visibly clicking and holding it you can also feel it.
The part isn't terribly expensive, like $60, but geez the labor to get this out looks incredible. Definitely a weekend project for me.