Ok, so I'm trying to get through the checklist on my 1985 380SE Diesel (converted), I've been trying to get the heat to work properly, I'd also like to fix the A/C but figure thats a waste of time until the rest of the system functions correctly. I had asked this question a while back somewhere else but seemed to hit a dead end with no further instructions. So without further adieu, the issue at hand.

Symptoms:
1. Blower will not start unless Bi-level, or Defrost are selected first. After one of them has been pushed the other two setting will work, as will the automatic and hi\low settings.
2. regardless of the setting selected, none of the vents change. Seems the vents will not change from the defrost setting.
3. Temp wheel functions as it should (sort of) and blower speeds up and slows down in relation to its position. I have noticed that after full heat it doesn't like to go full cold. Thinking this ties into symptom 2 and guessing that the heat flap isn't closing.

Actions taken so far:
1. CCU unit first re-soldered, and then changed out with a unit from the wreckers with no change in symptoms.
2. Mono valve replaced with good unit from the wreckers. Thats how I got heat.
3. Tested Pods from gang valve, these were the initial results:

1: holds at 20inhg
2: Bleeds quickly down to 10inhg and holds
3: can only pump up to 5inhg and then drops to ~2-3 and holds
4: holds at 20inhg
5: Bleeds quickly to 0
6: bleeds slowly to 4inhg and then holds

I replaced the recirc and fresh air actuators, and the legflap one doesn't seem to leak anymore so that should all be good. But I'm still having problems. The system still will not activate unless on bilevel or defrost, and it still will not open or close flaps. The heat works on defrost, or somewhat on bi-level. On bilevel it doesn't seem to heat well, it warms slightly as I turn the the dial up, then when I click it over to max I get excellent heat. So there's still something amiss. But this is not consistent. Somedays it heats adequately other days I freeze, then still on others (less often than the other two) I bake... More often than not though it just seems to heat feebly.
I'm beginning to think that it could be the climate control amp or something to do with the whatever is supposed to keep the system from turning on before the coolant gets warm. Since this was a gasser at one point and had some of the harnesses changes when it became a diesel I'm also wondering if there is anything that could have been disconnected. Any Ideas????

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2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

I'm not as familiar with what year, what system is supplied on the 123, so forgive me a bit. If you have a monovalve, you have the ACC III and will NOT have an amp (or the dreaded servo). This is a good thing, but also suffers from similar issues. My guess is you have a vacuum issue for starters. I also am concerned about the cold-start lock-out for the blower. The klima relay will need to be considered, although low on the list in my guess.

You have verified leaking actuators, and fixed some, but what supply vacuum do you have in inches/Hg when running? You need a minimum of 10-16" to function properly. Any leakage will hamper the function of the system. Also, I suspect your temp sensor chain (inside, ambient outside).

A thorough read of the manual may illuminate you to the workings of your system, and should be available online. If not, you can glean a great deal from the R107 AC III info, which is the system I am most familiar with. It is available online at startek, MB's website. Look at Benzworld.org - Mercedes-Benz Discussion Forum in the 107 forum for the stickie, EGv107 for a link to teh online manual, then navigate to any of the 560Sl's for a good read on the Ac III system.

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?

Classic symptom of bad CCU


Did these actions result in a "Known Good CCU"™? Popping in a finely aged and pickled unit from the wreckers is about as effective as stabbing the original with a soldering iron. So, until you are working with a "Known Good CCU"™ your troubleshooting is an exercise in futility.

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'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

my ccu started doing some of these same things a while back. must be a local thing

i don't have the patience to try and bother with it as far as you have. good on ya!

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1981 300SD - 283,000 KM's at purchase, 360k+ now. Engine replaced at 311k. 16" CLK wheels, w126 gen II cosmetic upgrades, late w126 leather interior. RIP. Parted and gone due to fire

1987 300SDL - 243K miles and counting. In winter hibernation!

2001 Ford F250 Super Duty "Platinum Edition" Lariat 4x4 7.3L turbo diesel, 295k+ miles, various mods for reliability and performance.

@WDBCB20 I realize it it technically possible for both the board I re-soldered and the one form the wreckers to be faulty. But it just seemed unlikely that both would display the exact same symptoms. Thats why I was leaning toward it being something else.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

That's a CCU relay problem. Cleaning the contacts on the relays is a good place to start.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

To save yourself some time and money I would send the push button assembly to GDL. Definitely don't buy a new one. I did and 5 years later I have the same problem you mention. I've got faith in Peter that he can fix it in such away that it will not break again and it will probably be cheaper than any other choice.

If you are able to get one working let me know how you did it. I've tried resoldering and cleaning the relays to no avail.

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1984 300 SD 384,000 Miles

Its amazing how many folk will gravitate to the most expensive item on the list and declare, "That is it..." Maybe it is, but you got other problems to sort out first that have NOTHING to do with the blower/panel function. You got to fix/plug the vacuum issues first!

Let me re-address acouple of issues directly, assuming ACC III:
This is by design, if the lockout switch is not functioning... Originally, your system was equipped with a temp sensor that would prevent the blower from functioning at coolant temp below 40C. Since the engine has been changed, what provision for this circuit was provided? This is explained in the manual i referred to.

This is possible if the system vacuum is low, or leaks. Usual culprit is a torn diaphragm in the pod, either in the defrost dual-action, or center vent. Can also be other leaks. Have you measured your vacuum when engine running? As this car now has a diesel engine in it, how's you vacuum pump? Until you sort this out, a panel is worthless... Some wwill say a panel can cause this, and I will not dispute. The panel; however, contains 3 separate devices; blower control, temp control, and mode (flaps)... These are available separately.
Here I'm not sure on your model, but I am not aware of a flap for the heat. The monovalve regulates the hot water... It defaults to open (heat) and is in heat mode when de-energized...

ok... an accepted thing to try... No guarantees as some have mentioned.

May still not be a good unit. rebuilt aare available, or you can rebuild yourself for around $40.00 Then you'll know for sure. It may still be letting fluid thru. The fact that the temp does cool down some tells me the panel is working... At least partly as the monovalve has to be energized to stop the flow of water.
I can't emphasize enough... fix the leaks or plug off the leaking circuit. Until sorted out, forget about testing the panel because you can't without a dedicated tester for the panel.

System, or blower? How much supply vacuum do you have?
Is the sampling hose for the inside temp sensor in good shape? Max detent bypasses the temp control circuit and supplies full heat.
This sounds like poor regulation due to sensor issues. There are at least two: an ambient in the heater box, and one usually in the dash or somewhere else in the interior of the car (don't know on the model you have)

No amp, and bingo on the coolant temp lockout.

Granted most of my knowledge comes from rebuilding a 107 system, but I researched others during the project. All I wrote above is rubbish if you have the AC II system with the amp and servo.... well, not all.
Best of luck to you...

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?

The described symptoms do not implicate the low temp lockout switch. They are a perfect fit with a CCU relay issue.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I think the manual disagrees with your statement concerning the lockout switch... of course, this is from the ACC III for the 107...

Attached Thumbnails

 

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?

There is no disagreement whatsoever. Note that the problem is not that the fan doesn't run; it just doesn't start in two modes. Those modes utilize a different relay than the two modes in which the fan does start. Additionally, the lockout switch only functions when heat is called for; evidently the FSM euphemism for that concept is "undesired cold air." For sure, the no start condition being present in all temp selections would contraindicate the cut-out switch.

I had the same issue even though my cutout switch is bypassed to a permanent ground. Cleaning the relay contacts solved the problem.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Not against cleaning relay pins, fuse ends, etc...
I'm thru with this... I'm not gonna debate "start" and "run", etc. The manual goes on to say if def selected first, then the other fan functions will work. Regardless, your experiences may prove to be his problem, although he has a lot more going on that need correcting...
Peace-Out

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?