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  #1  
Old 05-09-2013, 11:49 PM
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Not so amused
 
Join Date: Apr 2010
Location: West Quebec
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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
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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  
Old 05-10-2013, 01:05 AM
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Quote:
Originally Posted by Zacharias View Post

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
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  #3  
Old 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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  #4  
Old 05-10-2013, 12:43 PM
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Location: West Quebec
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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
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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  
Old 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  
Old 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.
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  #7  
Old 07-08-2015, 11:42 PM
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Quote:
Originally Posted by desertmike View Post
Did you fix it? What was the problem
I replaced the monovalve insert as I discovered I had one in my parts bin. It was fine after that.

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.
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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  
Old 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?

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  #9  
Old 07-08-2015, 11:58 PM
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Join Date: Apr 2010
Location: West Quebec
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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).
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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  
Old 07-09-2015, 09:49 AM
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Location: West of Ft. Worth. TX
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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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  #11  
Old 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.
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  #12  
Old 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  
Old 07-10-2015, 02:07 PM
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Originally Posted by SD Blue View Post
Thank you. I've bookmarked that for when I get back home.

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