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#1
02-16-2009, 10:12 AM
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300D climate control question
When the temp control wheel it at max, I get a lot of heat. When I back it off just past the detent to lower it a bit, I get almost no heat. What's gone bad? Where should I start?
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked 
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#2
02-16-2009, 10:58 AM
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I'd guess it's the wheel temperature sensing mechanism itself. At full heat, it's not sensing the temperature anymore but just blasting with everything it has independent of ambient temp in the car.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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#3
03-28-2009, 10:14 AM
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Fixed it! After removing the ACC, I saw that the temp dial is a module that unplugs, with a circuit board held in with 4 brittle plastic clips (not sure if detailed enough in the pic), After removing the board, I wiped off the oily gunk on the silver plated traces and then used a pencil eraser to further clean the traces and the wiper contacts on the rotating wheel. It now works! I can control the temperature yippee!
Does anyone know how the temp wheel control the heat and A/C (currently not working)? In heat mode, does it control the duty cycle of the mono valve? Does the FSM CD cover the ACC and does it have a schematic for it? I need a good manual for this car! 
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked
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#4
03-28-2009, 10:28 AM
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The FSM does have a schematic of the circuit, but it's cr@p. Hard to see all the lines. In fact the entire module schematic is in there. Look under the Climate Control section. Tells you how to test it too.
The temp wheel is really a variable resistor When the air temp sensor (thermistor) in the dash matches the resistance of the thumbwheel resistor, the system is balanced and the relays in the control unit set the blower speed to low, and minimize flow through the monovalve. When it's out of balance, the fan speed is raised and the monovalve circuit kicks in. (Very basic explanation.) HTH
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mjk '84 300SD 119KMi (Liesl der Diesel) '84 300D 326KMi when the oil left (former parts car) '82 300SD 253KMi (new parts car)
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Linear Mode
