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  #1  
Old 09-19-2018, 07:12 PM
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Join Date: Oct 2008
Location: Washington D.C.
Posts: 263
Mono-valve issue? AC blows hot

Started having this issue with my 82 300D turbo with automatic climate control..the AC blows cold when i get in the car...then if I park the car and turn the AC on again...it blows hot air. If i go back to the car the next day, then it blows cold again...really thinking this a monovalve issue but not sure..any advice guys?
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1983 300 Turbo-"Nora"
1983 240D Auto "Lucia"-slowest on earth-1st love
1985 300 Turbo-Blue Goose-slowly plucking parts

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  #2  
Old 09-20-2018, 07:40 AM
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Join Date: Oct 2011
Location: Columbia, SC
Posts: 3,180
That sounds like a good place to start. It could either be an electrical problem with the valve controls, or a mechanical problem within the valve.

Remember that if the monovalve is de-energized, it defaults to the open (passes fluid) mode. Also remember that the control element for the monovalve is in the climate control box and it switches the grounded side of the circuit. So just because you measure 12 V at the valve does not mean anything.
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2014 ML350 Bluetec (wife's DD)
2008 E320 Bluetec (my DD)
2008 ML320 CDI (Older son's college DD)
1998 E300DT (Younger son's college DD)
1987 300TD sold to vstech
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1983 240D (body to greazzer, engine to t walgamuth)
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  #3  
Old 09-20-2018, 06:27 PM
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Thanks Jay...sounds like a good idea to swap it out.
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1983 300 Turbo-"Nora"
1983 240D Auto "Lucia"-slowest on earth-1st love
1985 300 Turbo-Blue Goose-slowly plucking parts

http://i117.photobucket.com/albums/o...ly15/mbsig.jpg
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  #4  
Old 09-22-2018, 11:29 AM
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Join Date: Aug 2010
Location: Sacramento, CA
Posts: 2,460
Try clamping off the heater hoses on both sides of the engine. Also feel the AC return hose
Fittings should be cold.
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