I would like to know what to check first if the heater does not turn on when I turn the temperature control all the way to 85. I have the blower at Auto-Lo and the temperature control at 85. The air coming out is still cool. The AC switch is turned off.

Thanks.
Omy

Place a stethescope or screwdriver or a sensitive ear to the servo u.nit under the hood. With the key on engine off (to facilitate hearing) have someone run the temp from cold to hot. Listen to whether the clockwork mechanism is driven by the internal motor.

If it doesn't then it probably will have a stuck servo but that also can take out the amp. Tell me what you find.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Hi Steve,
Pardon the ignorance. I enclosed a picture of the heating pump because I cannot locate the servo unit. (The attachment didn't work.) :-( Is it close to the heating pump or underneath it?

Also, when I turn the ignition on with the engine off, pressing the auto-lo button did not turn on the blower. Does this mean the servo was not actuated?

I do have the Service Manual on a CD and I tried hard to look for the servo but I am not sure where it is located.

Thanks for you reply to my posting.
Omy

The servo has all the heater hoese attached to it. It should be within a few inches from the aux water pump. It's the size of a small football. It has a ten line vacuum connection at the top and two at the bottom.

It should be on the passenger side.

With key on, engine off the blower didn't come on because you didn't have vacuum. The temp control will work anyway and the blower will come with vacuum (as the engine starts). You can do the listening test with the motor running but its harder to hear and I suspect you aren't going to hear anything anyway. (as I presume the system is stuck or motor dead.

BTW the device will park after running so you should be able to hear it then, also. (after you turn off the key - it should run till it parks - about 10-20 seconds - I think)

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Hi Steve,

I did confirm that the servo control is not functioning. I found a place on the internet that sells this part.
http://www.adsitco.com/catalog.html
Is this price reasonable, $359? Where else can I find one as a replacement? Or can the old one be repaired?

Is it easy to replace this? Is there anything I need to watch out for when replacing it?

Thanks again in advance.
Omy

The price you have found is good for a new part. You should try at this site and use them if the price isn't too high. If its a little more consider it your contribution to site maintenance. If we all do a little the benefits grow for all. BTW MB list is $600.

The replacement is fairly straight forward but you might wind up needing some of the hoses (good time to change them).

Another problem that you probably won't be able to tell about till done is whether the amplifier (controller) was taken out whenb the servo stuck. They have a clockwork mechanism within the servo that jams when any of the small teeth of the gears are lost. In these cases the amp often fries itself trying to move the servo. If the motor open circuited then there will probably be no other casualties. The amp is behind the glove box.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Just to update this thread, I replaced the Automatic Climate Controller of my W116 this weekend. I also replaced the Climate Control Amplifier.

This fixed the problem I had with my car not having heat even when the temperature dial is at max (85).

Thanks to all who replied to my question.

Omy