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Old 01-08-2002, 06:17 PM
Registered User
Join Date: Jul 2000
Location: Sunny Florida
Posts: 199
W126 Heat question

I am certain I have seen the answer to this question someplace, but the search did not turn up my problem.

The car is a 1989 560SEL, with 139K miles. In the brisk Florida winter today, (50 degrees), my heat will only blow through the defroster vents on the windshield. This is with the temp wheel set on hot, and the "econ" button pushed, fan on high speed. With the fan on low or Auto, I get no fan. I flipped around the buttons, hoping it would fix itself, but no.

As a side note, I left the lights on at work the other day and found my battery completely dead. Door locks wouldn't even open. I jumped the car and thought I was ok. Could there be something similar to the dreaded OVP in the climate control circuit?

I appreciate any help you can throw out there. Thanks!
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)
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Old 01-08-2002, 11:11 PM
Registered User
Join Date: Dec 2001
Location: LaPorte, IN
Posts: 400
Monovalve is a likely candidate. We recently brought an '89 560SEL to northwest Indiana from south Florida with identical symptoms. Best $30 or so I've ever spent, and a very simple repair. I learned all I need to know on the diagnosis and repair right here. Good luck.
Earl McLain
'89 560 SEL
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Old 01-09-2002, 01:09 AM
Registered User
Join Date: May 2000
Location: Greenville, NC
Posts: 533
Also before you do the monovalve job. a good coolant flush product (from MB dealer-$6.95) followed by the OE Mercedes coolant AND distilled ph neutral water made my W126 heat system work alot better.
1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

609 Certification
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Old 01-09-2002, 08:21 AM
Registered User
Join Date: Jul 2000
Location: Sunny Florida
Posts: 199
The monovalve got it. I had ordered a kit when I first bought the car, "just in case". After I got home from work, I poked around my junk in the garage and found it. Took not much time at all, after moving the diagnostic port out of the way. Blows hot air now, and, for the record, the vents in the center are not supposed to blow heat. I found this info in a wacky place - the owner's manual!

And I have flushed and replaced the coolant just this past spring, but that is good advice I agree.

Thanks for the help!
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)
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