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Old 05-17-2001, 09:43 PM
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Hi all!

Got a stumper here... need some help!!!!!

Here's the scoop... 84 MB 500SEL, rebuilt climate control pushbutton assembly - installed. Both temperature sensors (inputs to control assy.) replaced with new (one purely for cosmetic reasons, grill would not stay on). Also rebuilt that valve just in front of the firewall right middle side (forgive me, I forgot the proper name for it). Everything works as it should EXCEPT...

Temp control wheel set to 65 degrees - in car temp stays at 75 degrees. Temp wheel set to 80 - in car temp stays at 90... and so on and so fourth. The only setting that works properly is the max cool setting. The in car temp gauge has been verified and is correct, any ideas???

Thanks for the help!

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Old 05-17-2001, 10:00 PM
Ashman's Avatar
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Join Date: Sep 2000
Location: Sherman Oaks, CA
Posts: 4,748
Have you had your AC recharged?

Was it evacuated and replaced recently. Usually thats what will help you get ice cold hair is an AC recharge.

Perhaps the new sensors are faulty.

I'm not a tech, but I hope that helps.

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Old 05-17-2001, 10:43 PM
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forgot to tell that ac system is perfect... from clutch to condenser... works fine in max cool position

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Old 05-17-2001, 10:50 PM
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And if the interior temp sensors are operating as they should, then there must be something wrong with the physical temp switch...?
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Old 05-18-2001, 09:34 AM
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
It sounds like the temperature dial wheel is not 'aligned' with the thermal element it activates.

This is the way I think it works. I could be all wet, and am not an MB tech, but here goes.

As you turn the wheel to warmer or cooler it mechanically moves the on/off point. From what you describe, 75=65, 90=80, the dial 'reads' 10 degrees off from the element setting. Now, if that is so, I don't know if there is a mechanical adjustment to re-calibrate the dial or not.

How new/recent is the rebuild on the climate control pushbutton assembly? Perhaps it wasn't properly calibrated during rebuild. Try talking to the supplier of the rebuilt control, tell them it's 10 degrees off everywhere and see if they offer to re-calibrate it for you.

Good luck and BCingU, Jim
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Old 05-18-2001, 09:51 AM
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I would like to add something to this good list of things to check. On your model I don't know where the interior temp sensor is located. But find it and ensure that the air tube that provided interior air to the sensor is not deteriorated, collapsed or otherwise blocking air flow to the sensor.

Additionally, I don't think your car has one, but on the 124 cars there is a small fan that feeds air to that sensor. This fan runs any time the ignition is on. If it is worn out, it will cause similar problems.

My $0.02
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Old 05-18-2001, 08:19 PM
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Join Date: Jul 2000
Location: Toronto, CANADA
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Great idea Larry! The air temp senor for interior air in the w126 is overhead above the rear view miror in the light console. There is what looks like a small plastic grill. Interior air should be flowing into this area.

Follow this link to a great article on MB climate control systems.

Good Luck, you'll be needing that AC for sure right about now.
Jason Priest
1999 E430
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Old 05-18-2001, 08:28 PM
Q Q is offline
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Read this article...
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Old 05-19-2001, 07:17 AM
Posts: n/a
Thanks for all the good advice!!
I spoke with the rebuilder of the control unit about the problem and he said he has never heard of such an instance and the wheel can only be installed one way, he did offer to recheck the controller for me at no charge but I am not so sure this is the problem. I had previously checked the airflow across the car temp sensor... but rechecked it again... still good. I am now going to perform the checks in the article Q posted... hope that leads me somewhere

Thanks again for all your help!!!
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