Here goes. My heater in my SLK320 has been blowing hot in every selector position on the driver side only. I picked up a replacement control dash unit. I have the same symptoms. It's weird.

If you set both of the temperature controls to full cold, the passenger side blows cold and the driver side blows a hot-cold mixture. If you move the passenger side to warm or hot, it responds correctly blowing that setting. If I move the driver side toward warm or hot, it gets hotter only. So it never adjusts to a cold only setting no matter what I do. Always blowing hot air from the left side of the system is ridiculous and I need to solve this.

Both the new and old controls act the exact same way. I think the valve on the heater hoses is acting up since the cold never goes off on one side. I tried tapping on the valve control on the heater hoses and nothing changes. I think one side is jammed or just dead.

What say you?

 

Hi BikerDrew,
Never had any probles with the Climate Control on either of my MS cars however the system is sufficiently simple that I don't think you should have any trouble locating the cause of your problem.
As I understand it the SLK has a double HEATER matrix and a single AC Evaporator.

The HEATER matrix has 1 inlet tube and 2 outlets which are controlled by solenoids near the top of the front suspension strut. (Not too sure anout handing between USA and Euro but expect the solenoids to be on the Right (Passengers side) in the USA.
The single inlet is on the opposite side of the firewall to the dual outlet.
I think you have diagnosed your own problem correctly.

try this simple test.
Set both temp wheels to cold with AC off (EC).
Start engine from cold. Once the engine is warm the two return pipes should still be cold. I suspect that you will find one is hot which will confirm your diagnosis that the solenoid is stuck OPEN.
Next check whether there is voltage to the solenoids. Not sure if they are NO (Normally Open) or NC (Normally Closed). However there should be symettry between the supply to the two solenoids. Assuming that this is the case then the valve must be faulty.
The valve can be dismatled so there is a possibility of a repair but since I haven't taken one to pieces I have no idea what you will find and to what extent it is repairable.

Hope this provides what you are looking for.
Only wish somebody would answer my questions!!

Stuart.

 

This describes what I found when examining the system. I think I will try pinching off the outlet hose on one side or the other, and see what happens. It would seem that a partially open valve would create the always hot symptom.

Thanks for the reply![sm=grin.gif]

 

Hey Drew!

Here's a DIY on disassembly of the Duovalve. Its on a W210, but I believe its the same unit.

http://mbclub.co.uk/forums/showthread.php?t=26888

 

Great info from DesignoSLK Drew. What did you find, and is it working correct now?

 

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The problem is on the heating side, not the evaporator.

Stuart

 

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[IMG]local://upfiles/1/F603E3388A91445BB38EFE959BE6F716.jpg[/IMG]

[IMG]local://upfiles/1/F0A854AB00EA4CE0BD63D07F617189A1.jpg[/IMG]

 

I will examine the system this weekend and get back to everyone. Thanks to all who helped![sm=groupwave.gif]

 

I repaired the solenoid by cleaning the brass pistons. Now the system works! [sm=happy046.gif]

Just think of all the $ I saved. Thanks for all the help! You guys rule. [sm=icon_rock.gif]

 

PLEASED TO HAVE BEEN OF ASSISTANCE.
IF ONLY I COULD GET SOMEBODY TO ANSWER MY QUESTIONS!
STUART