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Old 05-08-2000, 12:40 AM
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Join Date: Jan 2000
Location: ny, ny
Posts: 112
Now it seemed to happen most recently. There are three push button control that controls the temp of the climate.
The button marked a/c does not turn on the a/c it seems to not work as of recently, the other button which appears to be a heater button works and it actually turns on the compressor but only allows cold air thru the middle vents. Hot , Hot air comes thru the side vents.
Ofcourse the thrid button would be the recycle button.
Why does this occur?
Anyone experience a similar problem?

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Old 05-08-2000, 07:48 AM
Posts: n/a
I expect that you will find the problem to be either the monovalve that controls flow to the heater core, or the pushbutton control unit that controls the monovalve.

Good luck,

Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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Old 05-08-2000, 09:33 AM
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Join Date: Jan 2000
Location: ny, ny
Posts: 112
Larry i have no clue as to where the monovalve is located on my car, can u give me a clue and also do u mean the push button unit in side the car. It seems difficult to remove.How do u remove it.


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Old 05-08-2000, 09:39 PM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
As the W201 (190's) don't have an electric heater valve(mono) & all of the system operates on vacuum supply & demand, any vacuum leak will cause heater to stay on.
Since the center vent allows only fresh & or air conditioned air you won't feel the heated air there.
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Old 05-08-2000, 09:41 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
To sum it all up, there is one of two possiblities. 1, you have a vacuum leak (under the battery, red hose)
2, the potentiometer for the blend door is not reading.

Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
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Old 05-08-2000, 10:42 PM
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Join Date: Jan 2000
Location: ny, ny
Posts: 112
Ok but when you press a/c button the compessor does not kick in, only when the button above the a/c button is depressed does the compessor come on thus providing a lil cold air thru the middle vents, nevertheless the side vents are blasting hot air.
So my question is it still a vacum problem or a switch control problem.Also where is the potentiometer?

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Old 06-05-2000, 08:47 PM
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Mr Benz, I have exactly the problem you describe with the a/c on my '87 190D. When the dehumidify button (the one above the AC) is pushed, I get cold air (w/ compressor engaged) from center vents, but hot from outer. With AC button depressed, compressor cuts out after about 45 sec.

So I'm curious what you found out about your problem. Any answers from anybody? TIA

Oh, and thanks to Benzmac for help with vacuum control valve. Changed it today, and for the first time, the tranny shifts SMOOTHLY! Thanks.

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