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Climate Control , before I by Duovalve

1831 Views 7 Replies 7 Participants Last post by  lilbee45
I know this was talked about, but I just want to make sure once more before I change this part.

Heat works good through all settings, but sometimes goes crazy and starts blowing very hot air even at low TEMP setting, unless I press the COOL outside air button and then only center vents will do so.

When uing AC, Most of the times only the center vents blow cool, Defroster most always blows HOT and sides vents have a mind of their own, forcing me to only use center vents, meaning using a defroster in summer will sucks ass.

Sounds like an air distribution problem. Is it the DuoValve or the flaps not engaging properly.


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I was through the same problem with my black 1994 S420 (at 135,000 miles). I bit the bullet and bought a new duo-valve for over $400.00. It worked great...for about a month! Because I about had it with the hot air out the side vents, I unfastened the main hose going to the duo-valve and put a 3/8ths to 1/2 socket adapter in the hose about 3 inches from the end and put a hose clamp around it. After that, I had plenty of cold air from all vents. Once winter was on its way, I simply removed the socket adapter and enjoyed a warm and cozy car during the cold. The procedure is not very unsophisticated....but it is a sure thing. I sold the car a couple of years ago and the guy I sold it to does the same thing as the seasons change. Chasing a duo-valve is expensive...but fix was cheap.
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