Climate Control Servo or More? - Mercedes-Benz Forum

 
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post #1 of 9 (permalink) Old 03-22-2015, 01:21 PM Thread Starter
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Climate Control Servo or More?

I may need to order some parts for my 1980 300SD Mercedes. The car is in outstanding condition with 130,000 miles on it. However, I started running into problems with the air conditioner vents LAST summer.

First, I noticed the center 2 vents closed and would not open. So my air conditioner would blow cold air out of the defrost and the far left and right vents. Cold air was still blowing.

This winter I was able to adjust the climate control wheel and turn on the heat. Used the heat all winter. Over the winter I noticed there was a small 1 inch crack in the climate control server housing. I put JB Weld on the crack to keep it from getting worse.

Now that the weather has warmed up here in Atlanta, I tried to turn on the AC today. I adjusted the climate control wheel to 65 degrees, turned on the AC button and I heard the compressor engage, however the climate control servo did not turn.

Today I did some diagnostics and I disconnected the servo vacuum and power plugs and manually connected 12 volts power right to the 2 servo power pins. This successfully turned on the servo and I heard the gear turn all the way. Assuming this would activate the AC system I plugged the vaccum and power connectors back to the servo, got back in the car and went for a test drive. Still no cold air. Heat only from the defrost vent and side vents.

Seems like the system is stuck in Heat mode and the center vents are closed and defrost vent is always open.

Are these systems of a bad climate control servo or is there more to it? (vents not opening)

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1980 300SD
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post #2 of 9 (permalink) Old 03-22-2015, 01:42 PM
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I believe that the servo controls the position of the flaps. Like when the cabin reaches the desired temperature, it will move the flaps from "heat" to "cool." I think you are stuck in "defrost" mode which is sort of the default.

So I would say that unfortunately your servo has checked out. There is a modern replacement for the servo.

https://mercedessource.com/store/acc...tronic-upgrade

Good luck,

CT

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #3 of 9 (permalink) Old 03-22-2015, 01:55 PM Thread Starter
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yeah I agree I need to replace the servo but are you sure the servo controls the position of the flaps I was under the impression that the buttons on the climate control console control the position of the flaps it sounds like there may be more than just the servo being the problem. but if you're sure that the servo controls the vent flaps then this should be an easy fix by replacing the servo
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post #4 of 9 (permalink) Old 03-23-2015, 08:38 AM
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if you want , there is a way to totally bypass the servo using a heater valve from a 190e 201 . the only thing you will have heater on or off , no temp control .
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post #5 of 9 (permalink) Old 03-23-2015, 08:40 AM Thread Starter
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Will the air conditioner still work?
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post #6 of 9 (permalink) Old 03-24-2015, 04:46 AM
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Quote:
Originally Posted by agillot View Post
if you want , there is a way to totally bypass the servo using a heater valve from a 190e 201 . the only thing you will have heater on or off , no temp control .
Do you have any other details. As the owner of a 1977 300D, I am just waiting for the Evil Servo to fail and would like to be ready with a "work around". I would love to replace it with the more modern aftermarket unit but it cost $650!!

Baton Rouge, LA

1977 300D - My DD
2004 LS430 - Wife's DD
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post #7 of 9 (permalink) Old 03-24-2015, 06:39 AM Thread Starter
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I just talked with George Murphy at performance analysis and he said everything I described is a side effect of a failed servo. Center vents not opening are also side effect of failed servo. just ordered a new billet aluminum replacement and replacement amplifier.
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post #8 of 9 (permalink) Old 03-25-2015, 08:40 AM
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on every cars of that vintage , the dash flaps vacuum elements go bad , center vents are usually the first to go .this early climate control is a chrysler design , it is a lousy design and hard to fix . this is why the early cars with manual controls where the best , nothing to go wrong , you just moved levers by hand .
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post #9 of 9 (permalink) Old 03-25-2015, 09:05 AM Thread Starter
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can you tell me where the center vent flap vacuum elements are located? I'm going to replace them
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