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#1
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300D heater is either off or full blast?
My 83 300D heater is either off or on full blast! When the dial is on the lowest blue temp it is off but when I nudge it just a little beyond this off area on the dial it is full hot. Even with low fan, the car ends up too hot and I have to shut the heater off/on every 3 minutes. What gives, why isn't my heater gradual variable intensity? Is there something I have to replace or adjust. Thanks.
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85 300CD Signal Red/Tan sold 83 300D Manganese Brown 109K 97 E420 Midnight Blue 197K sold 98 BMW 328i Vert White 100K, sold 95 BMW 525i White 125K, sold 93 BMW 525iT Red 193K, sold 95 E320 Green Wagon 125K, sold 94 E320 White 127K, sold 85 300SD 156K Grey (Annie), sold 84 300D Lapis Blue 170K (Judy), sold 99 ML 320 Black (lease), 1998 C230 White (lease) 00 Honda S2000 Red (lease) 86 Mercedes 300E (sold) 84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold) |
#2
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Monovalve?!
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#3
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Check the wiring to the temperature sensor that lives in the top of the dash. If it has a broken wire or is unplugged, the CCU will be "confused."
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#4
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If the cold setting does the same (off or full blast) the foam hose that goes from the temp sensor to the sensor itself, behind the glove box, has disintegrated and must be replaced.
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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg |
#5
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I had a similar problem, a new mono valve did not help.
Follow the above advice, if the problem persists, let us know.
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83 SD 84 CD |
#6
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I'll check the wiring to the temperature sensor tomorrow in the daylight. I assume you go through the glove. I've turned off all my circle vents and only heat the floor and it's too hot. Toomany MBZ, did you fix yours?
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85 300CD Signal Red/Tan sold 83 300D Manganese Brown 109K 97 E420 Midnight Blue 197K sold 98 BMW 328i Vert White 100K, sold 95 BMW 525i White 125K, sold 93 BMW 525iT Red 193K, sold 95 E320 Green Wagon 125K, sold 94 E320 White 127K, sold 85 300SD 156K Grey (Annie), sold 84 300D Lapis Blue 170K (Judy), sold 99 ML 320 Black (lease), 1998 C230 White (lease) 00 Honda S2000 Red (lease) 86 Mercedes 300E (sold) 84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold) Last edited by edge; 11-13-2009 at 11:08 AM. |
#7
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Remove the glove box and you'll be able to see both the temp sensor, its wiring, and the foam tube that is supposed to connect it to the blower but probably has disintegrated. I suspect Mercedes used foam as an anti-vibration measure; you can use foam pipe insulation or a solid piece of tubing as you prefer. The blower sucks air in from the top of the dash over the sensor and, in theory, makes the sensor respond faster to temperature changes in the cabin. The sensor has two wires.
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#8
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edge, no. That car went to the crusher before I fixed that problem.
I will suggest pulling the CCU and check for cold solders, after you've followed the previous posters advice.
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83 SD 84 CD |
#9
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Quote:
Full heat should provide NO VOLTAGE while FULL AIR should provide 12Vs. I believe any temperature inbetween it cycles on and off. It seems to me this full heat problem people experience is usually an unplugged monovalve.
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2009 ML320 Bluetec 1985 300CD 1981 300TD Past Mercedes 1979 300TD 1982 300TD 2000 E320 4Matic Wagon 1998 E430 1984 300SD 1980 300SD |
#10
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Hi...I know my sensor is bad and the heat is unbearable. Anyone know the part number of have a link so I get the right part.
Thanks
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Paul 1991 300TE (280,000) 1985 300TD (432,000 miles - retired) 1976 300D (225,000 - retired) 1975 300D (165,000 - retired) |
#11
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Quote:
Jeremy
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#12
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If the heat is full off or full hot nothing in between and the means of temp regulation is via the monovalve, doesn't that mean the monovalve is working fine? Anyway, I had this problem with my 300D plus clicking sounds in the CCU. I took apart the temp dial to expose the potentiometer and cleaned it with brake clean, checked full range of the pot with an ohmeter to make sure I have full range of continuity, reassembled and no more clicking and I have control over the temp. YMMV
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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 |
#13
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Quote:
__________________
85 300CD Signal Red/Tan sold 83 300D Manganese Brown 109K 97 E420 Midnight Blue 197K sold 98 BMW 328i Vert White 100K, sold 95 BMW 525i White 125K, sold 93 BMW 525iT Red 193K, sold 95 E320 Green Wagon 125K, sold 94 E320 White 127K, sold 85 300SD 156K Grey (Annie), sold 84 300D Lapis Blue 170K (Judy), sold 99 ML 320 Black (lease), 1998 C230 White (lease) 00 Honda S2000 Red (lease) 86 Mercedes 300E (sold) 84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold) |
#14
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I've never heard why the factory chose to use a foam tube in this spot; my personal guess is that it deadens sound transmission and vibration from the blower to the dash, which would otherwise act like a drumhead. Lack of that tube would mean no airflow over the sensor, making the system response slow but I don't think it would make it go to the extremes you are seeing.
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#15
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Max heat problem still there but improved somewhat. It's primarily too hot coming out of the defroster vents adjacent to the front windshield. Arghhh!
__________________
85 300CD Signal Red/Tan sold 83 300D Manganese Brown 109K 97 E420 Midnight Blue 197K sold 98 BMW 328i Vert White 100K, sold 95 BMW 525i White 125K, sold 93 BMW 525iT Red 193K, sold 95 E320 Green Wagon 125K, sold 94 E320 White 127K, sold 85 300SD 156K Grey (Annie), sold 84 300D Lapis Blue 170K (Judy), sold 99 ML 320 Black (lease), 1998 C230 White (lease) 00 Honda S2000 Red (lease) 86 Mercedes 300E (sold) 84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold) |
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