'78 280ce Part Identification & Function (video)

[Ten13]

Hi again,

I need help identifying this part, and more importantly, to ask if this is functioning normally.

It appears to be connected to the heating system, and it oscillates (by vacuum) for as long as the engine is running. However, one day, I noticed it was not moving. Ambient temperature was about 83 degrees, and the car's coolant temp (indicated) was approx 175 degrees after a highway run.

It is connected to the aluminum box next to it (part of the climate control system?)

Disregard the exhaust leak - muffler coming from Germany! And, while I have you, is this normal valve noise? Sounds about right to me, but I'm not an expert (yet) with this engine.

Here's a link to the file on my dropbox:
https://dl.dropboxusercontent.com/u/47225258/w123%20part%20ID.MOV

Thanks, All!

[Idle]

You are looking at a heater valve. It takes a vacuum signal from your servo to regulate the amount of hot water entering your heater core.

This is moving constantly as it is trying to maintain the interior temp you have dialed into your climate control. If the interior needs more heat this opens; less heat and this closes off.

The valve and the servo above it seem to be operating as they should. In warmer weather they are not going to operate much since you will not be setting the climate control thermostat for heat.

This is a complex system. If you don't have the heating and a/c manual for this car you need to get one.. These show up on Ebay now and then and the manual takes all the mystery out of these systems.

[Dmitry at Pelican Parts]

If you're looking for a procedure guide for the heater valve, take a look at our DIY tech article below and please let us know if you have any questions!

Mercedes-Benz W123 Heater Valve Replacement | 300TD 1977-1985 | Pelican Parts DIY Maintenance Article

[Phillytwotank]

Not original equipment. Your looking at a part of this https://unwiredtools.com/accii.asp

very common upgrade to early w123s that came originally equipped with the ACC II climate control system, the "evil servo"(look it up)

If it is opening and closing like that i would assume that it is working properly. regulating hot water flow based on where you have the cabin temp selector set.

[Idle]

Originally Posted by Phillytwotank

Not original equipment. Your looking at a part of this https://unwiredtools.com/accii.asp

very common upgrade to early w123s that came originally equipped with the ACC II climate control system, the "evil servo"(look it up)

If it is opening and closing like that i would assume that it is working properly. regulating hot water flow based on where you have the cabin temp selector set.

I've rebuilt these evil servos and even though it has been over twenty years since I did so I seemed to remember everything went through the valve body in the base of the servo. I just figured this valve was something that came along later.

And these servos are not hard to rebuild. They are hard to keep in the correct order once you have taken them apart but they can be rebuilt. When I saw the cost of a replacement I didn't think I had anything to lose by trying to rebuild it.

[Ten13]

Originally Posted by Phillytwotank

Not original equipment. Your looking at a part of this https://unwiredtools.com/accii.asp

very common upgrade to early w123s that came originally equipped with the ACC II climate control system, the "evil servo"(look it up)

If it is opening and closing like that i would assume that it is working properly. regulating hot water flow based on where you have the cabin temp selector set.

Thank you @Phillytwotank... That's exactly the system installed in the car. Bookmarked in case of future need!