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#1
05-09-2013, 11:49 PM
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Sudden hot air issue, w123
At first I thought it was my imagination... but when the temps cooled this evening there was no mistaking it. I have heated air blowing from the ACC system on my '85 300d. I tried all the (non-defrost) settings and it does the same thing. It seems to be getting gradually worse. (My AC has been inop since late last summer so that is not in the equation.) Tried moving the temp wheel to minimum then back to cool settings, no difference.
I looked up some old posts and I found suggestions but no feeback on solutions. From what I read it can be: - bad temp wheel - disintegrated tube to dashboard temp sensor - bad monovalve Anyone care to add detail or suggestions? I have to live with it until the weekend and it's crazy hot here right now.... Thanks
__________________
 Mac 2002 e320 4matic estate│1985 300d│1980 300td Previous: 1979 & 1982 & 1983 300sd │ 1982 240d “Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22 
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#2
05-10-2013, 01:05 AM
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Quote:
__________________
 All Diesel Fleet 1985 R107 300SLD TURBODIESEL 2005 E320 CDI (daily) LOTS of parts for sale! EGR block kit http://www.peachparts.com/shopforum/diesel-discussion/355250-sale-egr-delete-block-off-plate-kit.html 1985 CA emissions 617 owners- You Need This! Sanden style A/C Compressor Mounting Kit for your 616/ 617 For Sale + Install Inst. Sanden Instalation Guide (post 11): http://www.peachparts.com/shopforum/diesel-discussion/367883-sanden-retrofit-installation-guide.html
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#3
05-10-2013, 01:16 AM
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Crazy hot in West Quebec? How can it be?
The monovalve gets a pulsing/constant ground from the temp controller. Try attaching a meter to one of the leads and see if you get a variation when adjusting the temp control wheel. If you see a change, then it's likely to be the monovalve.
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Sam 84 300SD 350K+ miles ( Blue Belle )
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#4
05-10-2013, 12:43 PM
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Everyone's a comic, EH?
Glad you all find heat in West Quebec so amusing
 .Actually it's been in the low 80s here for a week... 50-60 daytime would be seasonal. Doesn't take much hot air output out the vents to make things uncomfortable in heavy traffic. Will test for a temp wheel signal at the monovalve and check the tube for the dash sensor this weekend. As I installed one of the MTC monovalve kits 2.5 years ago, which others seem to be having issues with in far less time, I am wondering if that is the culprit. Cheers
__________________
Mac 2002 e320 4matic estate│1985 300d│1980 300td Previous: 1979 & 1982 & 1983 300sd │ 1982 240d “Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22
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#5
07-08-2015, 08:09 PM
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Did you fix it? What was the problem?
Where is this dash sensor?
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#6
07-08-2015, 10:48 PM
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desertmike... pop your dash insert and clean all the bulbs or replace them with LEDs.
Cleaning the dimmer pot on the lower right in the rear might help too.
__________________
1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#7
07-08-2015, 11:42 PM
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Quote:
On your '85 there is a tube that runs down from the little vent in the center top of your dash to the sensor for cabin temp. The tube can disintegrate over time, meaning that the sensor is getting a wrong reading.
__________________
Mac 2002 e320 4matic estate│1985 300d│1980 300td Previous: 1979 & 1982 & 1983 300sd │ 1982 240d “Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22
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#8
07-08-2015, 11:44 PM
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I'll check that sensor and tube. Is there a good way to do that? Is the tube supposed to go to the CCU?
Sent from my XT1060 using Tapatalk
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#9
07-08-2015, 11:58 PM
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Honestly I haven't had to deal with that. I am not sure where the sensor actually is.
I think the tube on my '85 was replaced (first owner - to 2010 - took it to the dealer for everything).
__________________
Mac 2002 e320 4matic estate│1985 300d│1980 300td Previous: 1979 & 1982 & 1983 300sd │ 1982 240d “Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22
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#10
07-09-2015, 09:49 AM
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These links should help you sort things out:
Mercedes Service Manual Source, CD/DVD/Paper Mercedes-Benz Model 123 - Disc 2
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Sam 84 300SD 350K+ miles ( Blue Belle )
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#11
07-09-2015, 03:22 PM
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The rubber/foam tube from the dash temp sensor goes to the suction of the cabin blower. It is just to maintain air flow past the sensor. The foam falls apart. Many posts w/ photos. It will still work without the tube, just not optimally.
__________________
1984 & 1985 CA 300D's 1964 & 65 Mopar's - Valiant, Dart, Newport 1996 & 2002 Chrysler minivans
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#12
07-09-2015, 06:32 PM
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About 1 month ago I had constant heat coming out even on the coolest setting. I purchased an mtc monovalve put it in and still had the issue so I cleaned the screen on the old one put it back in an now no heat coming out. My A.C. is not working I roll down my window for that but at least I dont have heat coming out like before. You could also try pinching off your hose running to heater core to verify if it is a bad monovalve. I really cant explain what made my old one work but it does and I'll leave it at that.
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#13
07-10-2015, 02:07 PM
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Quote:
Sent from my XT1060 using Tapatalk
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