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  #1  
Old 11-21-2002, 11:06 AM
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W123 climate control stuck on max heat!

The heater in my 1984 300D suddenly decided to only put out maximum heat. Turning the temp wheel has no effect, even set at "Min", neither does turning on the AC... full hot, all the time. This is the OPPOSITE of the infamous monovalve problem, besides my monovalve is new as of 1 year ago. Any ideas what would cause this? It was working perfectly until now...



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Old 11-21-2002, 11:39 AM
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Based on the exact same thing happening on my W201, I would suggest that you have a vacuum leak in the feed for the monovalve. Cheers, Andrew Seidel.
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Old 11-21-2002, 11:45 AM
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Hmmm... I think on my 123 chassis, there is only an electrical connection to the monovalve. I'll check that though.... thanks!
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  #4  
Old 11-21-2002, 12:46 PM
LarryBible
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If the diaphragm ruptures, you are looking at max heater flow. It only takes five minutes to pull the cover to see if it is flooded.

Good luck,
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Old 11-21-2002, 06:37 PM
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Max heat is caused, in addition to what Larry suggested, by a damaged foam tube behind your glovebox. This tube conveys air from the dash vent to the control sensors down in the fan area. If the foam falls apart, there is no airflow to the sensor(s), and the heat cranks up full blast!!!

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  #6  
Old 11-21-2002, 07:05 PM
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Mine was just the opposite. I got minimal heat when the diaphram failed. Maybe there is more than one way they can fail. Why not just hook up a voltmeter to the monovalve plug, spin the temp control from full cold to full hot and see if you are getting power. Make sure the keyswitch is on(I'd call it ignition but PEH would object - rightly so).

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