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  #1  
Old 12-05-2006, 12:59 PM
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Interesting Duovalve Observation

I had a similar problem that many have posted about. Duovalve sticking causing Hot air on drivers side vent while A/C comes out other vents.

It is interesting that when the duovalve goes it seems always to be on the drivers side, no one complains of the reverse, the passanger blowing hot with the others working well.

I just wonder why this happens when both of the valves (in the duo) are identical, why does the drivers side one go? Is it heat related since it is closer to the engine. Just bugs me?

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  #2  
Old 12-05-2006, 01:40 PM
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My duovalve unit went out and I got cold air on driver's side and heat for the passengers. '92 300SE.

Of course, I was wanting heat in this situation - possibly you're wanting the reverse?
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  #3  
Old 12-05-2006, 03:11 PM
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Location: Tucson, AZ
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when my 94 c280 duovalve it was cold on drivers side and heat elsewhere.
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  #4  
Old 12-05-2006, 10:05 PM
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Well, it seems like all four of us in this thread so far have had the same symptoms. My duovalve was replaced today and it also was putting out cold air on the driver's side but hot air on the passenger side.

Anyone know of a strategy to keep these working longer? I am wondering if monthly activiation of the heating system during the warmer months would help. I don't use the heat much from April to November.

Doug
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  #5  
Old 05-24-2008, 05:04 AM
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1995 W140 S350
When set to Air Conditioning I occassionally get heat from the passenger side vents. It also causes my engine temperature to go from just above 80 up to around 100. (Possibly the AC compressor running full time trying to fight the heat?)

-Jim
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  #6  
Old 10-17-2008, 06:08 PM
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I think I figured out part of the reason why the engine temp went up when running the AC. My Air Conditioning compressor clutch was going bad. It finally locked up and took out the belt Monday the 13th.

I ordered the parts Monday afternoon. Fast lane did not stock the compressor so I had to get it from someone else. Compressor ($940), Receiver drier ($50), and a new belt ($30).

My mechanic was able to install it in a bit over the book hours. He does not work on Mercedes very often, but he does great AC work. 6 hours by the book for a total of $315.

I'm $1,300 poorer, but my car is back running again and the AC works great.

He also pointed out the Duo Valve that was staring me in the face for the last 10 months. My car does not have the rear heat controls, so the description of the location on http://v12uberalles.com/Rear_AC_System.htm did not apply to me. On the cars without rear heat it looks like the duo valve is right up on top in the engine bay near the power steering pump. It is right there in the open...

I think I will take it apart this weekend and see if the repairs at http://v12uberalles.com/Rear_AC_System.htm work for me.

-Jim

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I did 22,000 miles during the first year of ownership.
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