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Discussion Starter #1 (Edited)
Hello,

Working more on my '81 380SL. Tried searching but did not find anything along the lines with these symptoms.

I get no heat.

I have the "Climate Control II" version.

Set TEMP wheel to max. Run car for 10 minutes to warm it up.

If I press the DEF button the flan blows but only cold air comes out the defrost vents.

If I press the bi-level, no fan blowing.

If I press the auto-low or auto-hi, no fan blowing at all.

If I press the A/C on/off rocker to ON then it activates the fan.

In a nutshell, the fan only blows on DEF and ac ON.

Even when the DEF is blowing, its still cold.

I read in the manual that the DEF uses an electric switch to activate the blower; no vacuum used in that case.

Also read that "temperature switch" on the bottom of the regulating value will activate the heater vacuum solenoid switch which engages the blower; this is used for the "auto" modes.

So I might surmise that the temperature switch or the vacuum solenoid is not working since the blower does not activate in the auto modes.

What concerns me though is that in DEF mode it still blows cold. So does this sound like multiple issues?

And what places to start checking? Also, where is the heater vacuum solenoid? I can't identify it's position from the manual picture; I want to pressure test it.

Thanks.
 

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Sounds like a switch problem, and no heat could also mean the hot water valve is not working. Presumably by "solenoid" you mean the valve? The vac is part of it. Its in the engine bay on the firewall forward of the heater box- you'll see the rubber pipes in/out. I could be all wrong because my system is the older lever style. Good luck.
 

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Forum Administrator , RC Colas® & Moon Pies®
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My '81 had the exact same symptoms. I believe that if you keep punching the Bi-Level button, it will eventually make contact and begin to work again. At least that's what happened with mine. Other than that, your symptoms mimic mine exactly. You have a busted Climate Control Servo. Look closly at the round can shaped part beneath the trapezoidal plastic top and you will find a hairline or larger crack, rendering it inoperable. I'm told it's $2K from M-B for the original style (all bakelite/non-aluminum casing) and then there's the labor. You'll likely also need a new amplifier since yours is probably burned up from the effort of trying to run the climate control with no success. Mine smelled like a cheap toaster in a retirement home where everyone only ate club sandwiches. It lives WAY up under the dash behind the glove box.

Here's what I did. Of course, I got mine with the Scottinsocal discount.

Dig gets buff Post #61

It's available from this and other places for similar prices and it deletes the Servo and the Amplifier in favor of a small unit that controls everything.

Don't Worry About Replacing Your AC/Heater Servo Ever Again!

Get Rid of It and Restore Your ACCII System to Its Original Function and
Keep It There with our Exclusive Digital ACCII Servo Replacement from Unwired Tools™

Part #: P83-500
Price:
$699.99 ea.


Mercedes® Air Condition Digital Servo Upgrade Unit, 107/116/123 Chassis

Or you can go for the degradeable model to maintain your car's "originality". My indie (Claude) told me that I would be replacing when it would fail yet AGAIN in less than 5 years.

Climate Control Servo - ALL : 1978-81 Adsit Company, Inc


Part Number: 083-0020
Rebuilt : $595.00 Online : $535.50
New : $0.00 Online Sale : $495.00
 

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I love climate control when it works right. Based on all the problems, the manual system on the 73 is pretty easy. If they hadn't used that goofy flap system in the heater box ! I took mine apart in 1988, now it needs it again. I glued Naugahyde on the bottom of the flappers and it probably degraded after all this time. So, that's on the list ! :(
 

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By then I won't remember doing it now, let alone 50 years back ! Course if I make 80, and am still driving my 73, guess that's a pretty fair run ! :D
 

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He has other problems. His servo is operational and he has heat.
should read, "...hot air thru def vents...", not heat. When in heat mode (actually, bi-level), the servo parks, obviously because the amp/sensor chain is snafu, I believe. Haven't been able to get back to the project.
 

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Discussion Starter #10
Hey Dig ... does the climate control servo operate the vacuum for the vent flaps, too?

My vent flaps do move; I have the instrument panel out and I can see a couple of the vacuum pots with arms into the vent panels (dunno what their called) and when I play with the panel buttons the vacuum pots move to change flaps. The fan still does not blow, however the vent flaps are moving.

Does this indicate that the climate control unit is at least operating to some degree?

It's been pouring rain here in Portland and I haven't been able to do any work; I got the other post from the "Ears" link and it has numerous steps which I want to work through.
 

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Discussion Starter #11
Hey Aussie ... thanks for that.

I do want to hunt down that vacuum switch to test it manually. I referred to it as "solenoid" simple because the manual does. It's the main heater vacuum switch that engages the blower for the auto and bi-level modes.

So ... silly question here at this point, open to everyone. I know we keep using the verbiage "vacuum" ... is all the "pressure" that is applied through-out the "vacuum" system ... is it all negative vacuum pressure? Is any of the pressure used, such as for door locks, etc, is it ever positive "pressure" ?

I ask because my only test tool is the typical hand held vacuum pump; it does not create positive pressure, just vacuum.
 

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One of the BW Old Guard/R129, W204 Moderator
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Hey Dig ... does the climate control servo operate the vacuum for the vent flaps, too?

My vent flaps do move; I have the instrument panel out and I can see a couple of the vacuum pots with arms into the vent panels (dunno what their called) and when I play with the panel buttons the vacuum pots move to change flaps. The fan still does not blow, however the vent flaps are moving.

Does this indicate that the climate control unit is at least operating to some degree?

It's been pouring rain here in Portland and I haven't been able to do any work; I got the other post from the "Ears" link and it has numerous steps which I want to work through.
I'll answer for dig...
Yes, the servo does re-direct vacuum to "some" of the vent functions. The push-button also energizes or de-energizes electrically operated vacuum solenoids for other functions. You really need to thoroughly read the section on ACCII in the manual to get an idea of the multi-functions...
 

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One of the BW Old Guard/R129, W204 Moderator
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Hey Aussie ... thanks for that.

I do want to hunt down that vacuum switch to test it manually. I referred to it as "solenoid" simple because the manual does. It's the main heater vacuum switch that engages the blower for the auto and bi-level modes.
#19 on the schematics is the one I think you are referring to...

So ... silly question here at this point, open to everyone. I know we keep using the verbiage "vacuum" ... is all the "pressure" that is applied through-out the "vacuum" system ... is it all negative vacuum pressure? Is any of the pressure used, such as for door locks, etc, is it ever positive "pressure" ?

I ask because my only test tool is the typical hand held vacuum pump; it does not create positive pressure, just vacuum.
All negative. Some vacuum motors (pods) in older units had vacuum on each side of the diaphragm, and newer use springs, to make the actuation 2-way, ie in and out.
 

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Discussion Starter #14 (Edited)
Yes, 19; main switch. Dunno where I got "solenoid" from.

Is that located under the dash behind the control panel, or is it in the engine compartment?
 

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One of the BW Old Guard/R129, W204 Moderator
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Yes, 19; main switch. Dunno where I got "solenoid" from.

Is that located under the dash behind the control panel, or is it in the engine compartment?
"located behind glove box on cars with left-hand drive)"... In quotes, because a LOT of stuff is located thusly...

Happy hunting
 

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I'll answer for dig...
Yes, the servo does re-direct vacuum to "some" of the vent functions. The push-button also energizes or de-energizes electrically operated vacuum solenoids for other functions. You really need to thoroughly read the section on ACCII in the manual to get an idea of the multi-functions...
Thanks. I had the great good fortune to have a properly working panel with all vacuum systems functional and so did not have to deal with that aspect of the project. The UT digital module was a direct plug n play in my case.
 

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One of the BW Old Guard/R129, W204 Moderator
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Yes, 19; main switch. Dunno where I got "solenoid" from.

Is that located under the dash behind the control panel, or is it in the engine compartment?
I don't know if this helps or not. It is from a '79...
The green one on the left is #19, I believe, but they are numbered on the header...

I'm not sure, but i believe the picture has the unit upside-down.
 

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