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Old 04-17-2019, 01:52 AM
Registered User
Join Date: Feb 2019
Location: CA
Posts: 11
AC Clutch Does Not Engage 85 300CD

Been tracking down a few electrical issues in my 85 300 CD. The AC clutch will not engage when the climate control is set to full cold. The tach does not work either. The OVP relay and fuse is good. The AC is full is refrigerant. Not sure where to go from here.
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Old 04-17-2019, 07:04 AM
WTB: 94/95 E320 Wagon
Join Date: Oct 2007
Location: Charleston SC
Posts: 2,578
I do believe that your car is the only year of the 123 series that has a KLIMA relay. This relay compares engine speed to compressor speed, and then cuts out the compressor if the speeds don't match. Lack of working tach, if related to no engine speed signal, would prevent the AC clutch from engaging.
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC
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Old 04-17-2019, 07:57 AM
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Join Date: Jan 2002
Location: New Jersey
Posts: 3,762
Yeah, klima. Believe you can jumper the pins. Do a search.

I assume everything else about your system (refrigerant level, etc) is OK?
1981 240D (73K)
1982 300CD (162k)
1991 350SD (113k)
1998 Chevrolet S-10 ZR2 (62K)
2011 BMW 135i cv (14k)
2014 Honda Odyssey (6k)
2015 Honda Accord Hybrid (5k)
2008 VW Rabbit (70k)
2004 SAAB 9-3 (83k)
1991 BMW 318i (183K)
1983 300D (228K) (wrecked by at-fault uninsured driver)
1985 300D (233K) (now in FL)
1994 Acura Integra (188k) (Rusted out)
1992 Toyota 4Runner (72k) (Rusted out)
1990 Daihatsu Rocky (??) (No parts)
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Old 04-19-2019, 12:14 AM
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Join Date: Aug 2010
Location: Sacramento, CA
Posts: 2,478
In my 1985 300D, the clutch wasn't engaging because the evaporator temperature switch was bad. Its purpose is to turn off the compressor when the evaporator gets too cold (below freezing). Remove the passenger under-dash cover and you will see it.

My switch never engaged, apparently because the gas thermometer had failed. I could adjust the spring to switch on, but that point didn't change w/ temperature. A fairly generic part. I installed a new one for a 1970's Chevy. I posted probably last year w/ photos. My car also has the Klima box, but never dug into it. I think one thing it does is turn off the AC when accelerating. Of course, another thing that disables the compressor is the low-pressure switch on the filter/drier.
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans
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