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Old 04-27-2007, 12:51 PM
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Join Date: Mar 2004
Location: ILLINOIS
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W126 monovalve stuck open

Friend of mine has a w126(1990) with the heat on full blast.Climate control seems to be fine,however I suspect a monovalve failed,stuck open.My question is,considering that we go in the summer season and heat will be useless for the next 5 months...can you shut the monovalve manually and repair it in the fall?,just to stop the antifreeze from getting in the heater core for the summer.

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Old 04-27-2007, 01:09 PM
Join Date: Jan 2003
Location: Florida
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The monovalves are open by default, they are closed by electrical energy!
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Old 04-27-2007, 03:27 PM
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Join Date: Nov 2006
Posts: 60
Originally Posted by Peter Guenther View Post
The monovalves are open by default, they are closed by electrical energy!
Therefore it is probably not closing.
In my C280 I shut the duovalve and the heat disappeared - but the thermostat no longer could control the compressor. The car became a freezer...
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Old 04-27-2007, 05:36 PM
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Join Date: Sep 2006
Location: New Orleans LA
Posts: 93

check that you have power going to the valve and you can check it
by pulling just 4 screws it took me about 15 min to change and only a small amount of fluid loss
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Old 04-27-2007, 05:58 PM
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Location: Brandon, Mississippi
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Sometimes just cleaning them up (the internal sleeve) with some 000 steel wool will do the fix. There is very thin tolerances between valve walls. If he has used some anti-freeze stop leak prior to this happening he is going to need to flush the system.

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