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Old 04-03-2002, 06:23 PM
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MB 1990 300CE Automatic Air Conditioning Problem

My 1990 300CE puts out both cold and hot air at the same time. The hot air comes from the left and right side vents and on the left side of the center vent. Cold air comes out of the center vent in the middle. What could be causing this?

Someone told me that the board behind the AC controls is at fault.
If so, can reconditioned boards be bought?

Any help on this subject would be greatly appreciated!
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Old 05-02-2002, 09:55 PM
Registered User
Join Date: Feb 2002
Location: Alexandria, VA
Posts: 326
More likely, the blendor motors have failed. In my case, I disconnected the battery and reset my computer and it took care of it, but this is the exception...usually, a very expensive fix.
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Old 05-02-2002, 10:13 PM
Senior Member
Join Date: Apr 2001
Location: Baton Rouge
Posts: 485
It could be anything from the duovalve unit malfunctioning to a bad a/c pushbutton assy. Have seen both of these components fail and cause this problem . You would have to get a electrical diagram and stsrt troubleshooting.
euro 287
Mercedes Technician 7 Years (retired to Hyundai)
2000 Dodge Durango
98 Mazda truck
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Old 05-02-2002, 10:27 PM
David C Klasse's Avatar
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Join Date: Jan 2001
Location: Mission Hills in the City of San Diego
Posts: 2,352
I think that 99% of Mercedes climate controls experience warmer air from the side (dash) vents with age. I believe it is a vacuum leak, or some sort of air leak.
If you do a search, you'll find information on this problem; it's been discussed several times.
Good luck!
2006 E350 w/ 155k miles (Daily Driver)

1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
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1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)
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