Hello,

I am the proud new owner of a 1980 300TD. It has, so far, been all around a great car, except for one thing: It's cold. I've got no heater and no blower. This must be the most advanced (complicated) climate control system I've ever had on one of my cars. I'm not even sure where to start.

I didn't think it'd be a problem until Fall. When I bought the car, it's was mid-60s and sunny all day, I thought the worst was over. I was wrong, it's snowing right now. The lack on demist in the rain is downright dangerous, too.

So here's how it is:

I've got no blow from the vents, at least nothing I can control.

When the car is cold, I can hear the blower making a bit of noise (I'm assuming this Merc is like other European cars, in that the blower always blows a little bit, even when it's off).

The control panel does nothing. I can't even press in a few of the buttons.

I have some steam coming from the defrost and dash vents. I keep the dash vents closed and there's rags stuffed in the defrost vents to keep the windscreen from fogging up. There's a small leak from the heater core, I'm assuming this is the cause of the steam.

So I guess I'm wondering, since I'm new to this car, where I should start. I don't want to fire the parts cannon at it just yet, since time and money are not things I like to waste. My other cars have had completely mechanical heater systems, so I'm not sure where to begin.

There's the control unit in the engine bay, another thing in the bay, the blower motor, the control panel, the heater core. If anyone could share tests for these units or just general advice, I would be greatly indebted. I have an 82 parts car the ready, but have noticed that somethings with the climate system are different (the control panel and if the control unit is the same, it's in a different place and I haven't located it yet).

Also, if there is a method to swap or convert this system to a simpler, more mechanical system, I am all ears.

Thanks and sorry for the long post.

Okay, I replaced the blower motor with one out of my parts car about about 15 minutes ago. I now have a functioning defrost, but nothing else. I feel that I can now rule out the control panel. Where to go next?

You have the evil servo unit one the car, start google'ing and start researching. It is also called the acc II

The minimum things you need to do in order to get the system working with all the buttons, is to. Unfreeze the aux water pump near the servo under the hood. Pop the glove box liner out and replace the computer and air sampler tube. You also need to test the vacuum system and make sure there are no leaks.

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Urgh that servo thing sucks. I had a W123 in my teens, then ten glorious years with a 75 300D, another W123 for a while, then ten years with a Mazda, now another W123 and there was never not something wrong with the auto climate deal in all of the W123's, including the parts cars, and every single other one I've ever seen.

The PO in the one I have now just said "screw it" apparently and bypassed it in a manner that the Defrost button works normally, the Bi Level button blows heat only, and none of the other buttons work. I am going to consider myself lucky and just have the windows down in the summer.

I believe that Mercedes Source has some sort of manual controls kit you can buy, and that'll be the first "luxury" upgrade my car will be getting. Man I miss the dual manual controls in the 75. THe inevitable girl in the passenger seat could crank the heat on her side and I could have cool air on mine and everybody wins. Why would you ever "improve" on that?

Rabble Rabble Rabble!

All right that's enough complaining for now.

For my purposes, the whole system doesn't have to function as it did. Right now, the only button that works is the Defrost button. With it on, I get heat front the defrost vents and the far driver's side dash vent (go figure). The steam from the vents issue seems to be gone, although my windscreen is fogging up some with the heat on.

I would like to get it to this point: Something to turn the heat on (dash vents) and something to turn the defrost on independent of the dash vents. I don't need the AC or even the temp control wheel, heat or defrost on full blast without fan level control is fine.

I'll have to research into this, but I gone few parts and fewer dollars to work with. I have that 82 parts car with a functioning heater system, so hopefully I can make something work with those parts. I'm hoping the whole system wouldn't have to be swapped over, as I've never been good at wiring and I'd rather not pull my dash.

I know an Albanian fellow and Merc fanatic, who suggested that I remove the control unit in the engine bay completely and just run straight hoses for the coolant. He said that's what they used to do in Albania when spare parts weren't readily available. I'm not sure about this though, and thought I should get second opinions.

You can have the dual control on your 123. Find a 240D in the wrecking yard and transplant the manual system into your car. PeachPartsWiki: Auto to Manual Climate Control Conversion

Also leaking coolant is bad juju in the passenger compartment, the "steam" is major unhealthy to breathe.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Okay, I've been reading around. I'm confused as to whether the blower unit I replaced under the glove box is only for the defrost or not?

I understand about inhaling the fumes from the leaky heater core. It's not enough to create much of a smell. I'm going to have to wait before I can get a chance to take the whole dash out.

Sorry the posts are slow, getting approved and all that.

It blows for everything....vacuum pods control what vents air comes out of....the push buttons sends a signal to the amplifier behind the glove box liner, that then sends a signal to the servo under the hood...that then sends vacuum to the right pod to open the right vent...the right vents will also it open if the sensor tube is gone...because the amplifier cannot detect the cabin temperature...

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Anytime I had a leaky heater box, the windshield was coated with a film of coolant. You might have a good evaporator. If your car has been cold for a while, its probably just clammy and humid.

Well, I've located a 240D parts car in town and I think I'll just be making the swap to the manual system and doing the heater core all at once.

How many posts do you need until they don't have to be approved? I think my project thread was denied.

Well buy the whole car, because you'll need it. Swapping to a manual ccu is nice but it is a reallllllyyyyy big project. You need to swap the whole heater box from what I have read, and that means taking the whole dash out.

Here's a good thread

http://www.peachparts.com/shopforum/diesel-discussion/236087-300cd-240d-manual-climate-control-conversion.html

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Evil Servo service manual
Evil Servo, service manual - PeachParts Mercedes ShopForum

Evil Servo bypass
http://www.peachparts.com/shopforum/diesel-discussion/286770-evil-servo-bypass.html#post2567364

Maybe pictures will help. Trying to get my heater working. Where to start?
http://www.peachparts.com/shopforum/diesel-discussion/238588-maybe-pictures-will-help-trying-get-my-heater-working-where-start.html#post2029228


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__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

I checked into what was done with mine and that was exactly what happened. Currently I have hot defrost and heat with the Bi Level button and the other buttons do nothing.

That would be AWESOME!

That might be the best quick fix until I can get to that parts car.

Am I correct in assuming, that because I'm getting hot air, that the monovalve and aux water pump are functioning properly? Sorry, I'm having some trouble really understanding exactly how this system works, what it needs to function at all, and what can be removed for less luxury, but more heat. haha. Every car I've owned has just had a bunch of cables.

The heater pump generally has few issues, put a 2 amp fuse in the pump ground and ignore it.

There is no isolated mono valve on the evil servo system.

The large black box, in the engine compartment contains the plumbers nightmare.

This box has water valving, electrical switching, and vacuum switching.

It is famous for developing cracks/leaks inside the box = soaking electrical and vacuum with hot liquid or STEAM antifreeze = more damage.

There is a digital replacement option, basically the same price as a rebuilt Servo, but it has better durability/fewer problems.

If you plan to fully learn how it functions, I hope you have at least a few weeks free time for reading.


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__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/