Back from two weeks away visiting Tuscany in sunny Italia

We had planned to go down with the 43 but I'm happy the duo-valve destruction thing happened before leaving as the roads, apart from the paying toll roads in that part the region are very poor indeed, with certain roads just stones and a lot of.... DUST! It reminded me of my years living in Greece in the 60's.

Removing the old duo-valve was relatively easy (it was the original as manufacturing mark was 98') and the water tubes pulled off without any difficulty. It is rather tight in there and to gain a bit of space I removed two plastic tubes on the bit plastic housing with the ECU, diagnostic pin, some fuses (I wonder what they are all for ), etc. I also flattened a bracket with two protruding tabs which serve no purpose, apart from digging in your skin.

When comparing the old valve to the new one, I noticed two plastic tabs, one on each side of the solenoid valves. I wonder if this is done to avoid home mechanics dismantling the unit.

Before assembling the new duo-valve, I pulled off the rubber bobbins which hold the valve body on the bracket and smeared some silicone grease on the bobbins and to each three tubes. Getting everything back on was tight but with the silicone grease the tubes just slid on smoothly. Tightened everything and checked for leaks. I lost some cooling fluid but the expansion tank level was still OK. I'll check in a couple of days.

I strongly recommend mounting the left rear pipe first before getting the others on. It made thinks easier and try to keep the circlips up close to the end of each pipe when sliding them on to the duo-valve, as they have a tendency of sliding down the pipe to the bulkhead. You can't get fingers down there to bring them back up.

Total time was two hours doing this but I took my time with a cup or two of coffee, taking pics and checking that everything was assembled correctly.

 

duo valves do they adjust heat vs cold air from AC head unit or what?
is this an age related part that should be replaced for proper operating function?

 

From what I can guess they are exclusively for the heating, each valve for one side of the cockpit. Apparently they can stick and hamper correct water flow on each side. Also if your coolant is dirty and old, you'll have crud flowing around scoring the little pistons and blocking flow. I guess if the heater works equal on both sides and the coolant is changed from time to time with the correct fluids, you should not have any problems

In any case, the whine is still there and I need to get into and behind the footwell to check the vacuum actuaters.

 

buying new duo valves, were they cheap parts?

 

No! 300.- Swissies

 

who said it's cheap driving a Benz?

 

AHHH! HATE CHANGING A PART AND DOESNT FIX!!! HATE HATE HATE ITTTT

 

Interesting thing going on today....

After a two hour round drive on the motorway at legal speed limits, or just over, the engine runs a bit cooler with the needle pointing at 80°c on the gauge all the time. This is since changing the duo-valve last week. OK the outside temp is lower than normal, but has little influence to operating temp not unless the temp gets over 30°c. This is a bit weird that I thought I should bring it up.

 

vast majority of the time, duo valve can be disassembled and repaired as opposed to replaced. it just gets rusty and/or gunked up inside and becomes stuck or can't properly seal off the hot water, this can result in less than usual AC performance (having to cool off air that is being warmed up by the heater core)

 

Just read your comments from September...

I fully agree with you that the duo valve can be disassembled, cleaned and put together again with little hassle apart from making sure the electric connector is pulled off before you start taking it to pieces. Probably very true that if the duo valves don't close the hot water flow, this will cause the AC to perform under par.

 

So peeps, after being bugged with a high pitch shriek coming form the HEVAC, I finally got around looking into this issue and I believe I have finally found the culprit! Its the vacuum actuator for the footwell flaps (see #39 on the diagram in the first of the attached photos).

As I no longer have the flexibility of a "snake" to get into the passenger footwell, I had to remove different elements to gain a better access.

1. Remove the plastic cover under the dashboard on the passenger side
2. Remove the passenger carpet on the bottom and sides. To do this you need to remove some trimmings on the lower door frame
3. Remove the footwell heating vent (one screw)
4. After all this is out, use this occasion to clean out the dirt which may have accumulated down there. You may find some treasures also...
5. Remove the three holding nuts on the footrest sheeting and discover the TCU, perfectly dry in my case and two other elements: a rectangular box with a K11 sticker on it and a yellow top relay. I have NO idea what these are. Anybody have ideas?
6. Replace the footrest sheeting as it doesn't hamper access to the HEVAC region.
7. Switched on the engine and went through the different vent positions: Auto, bottom, top and bottom, face vent and bottom, screen. Quickly heard that the foot flap actuator was making the noise. I removed the two vacuum pipes and no noise any more.
8. Using a mirror to look up from the bottom of the footwell, I saw that the actuator was held on with a torx T20 head screw. Removing is a bit fiddly but can be done no problem
9. Discovered that the flap mechanism is clipped in the HEVAC unit somewhere and I believe that should remain attatched to the flap and you just need to unclip the axle on the actuator end.

The new actuator is on order at the local MB dealer and should be here tomorrow.

Next episode I'll be putting everything back together and fingers crossed everything works as it should do.

By the way, I strongly recommend you change the cabin air filter when doing all this work. It's easy to do when you have the extra space available. Mine was in there since 2012 and was rather dirty and starting to smell musty. New one is a carbon filter.

Also I recommend you remove the plastic protection cover under the fan motor (easy just two clips) and see what comes out of there. I had a pile of old leaves, bits of twigs, etc.

 

Wrong spare part delivered this morning so new # identified and ordered for tomorrow... The EPC diagram for these parts is not clear and even the parts guy at MB said he was also puzzled

 

"By the way, I strongly recommend you change the cabin air filter when doing all this work. It's easy to do when you have the extra space available. Mine was in there since 2012 and was rather dirty and starting to smell musty. New one is a carbon filter."

And if it's really dirty you will want to clean out the drain hole inside the engine compartment. Mine got clogged up with dirt, leaves etc.. and when it rained the water did not go out the drain hole and went inside the car! It made a nice little pond under the passenger seat and messed up the sensor underneath.

I took apart that plastic shield underneath the dash. Water was dripping like crazy and everything was wet. Filter was very very dirty. Zayed helped me with this and I found that drain hole. The passage was omg dirty and clogged. Cleaned it all out and tested it with buckets of water and no more water inside the cabin.

Below I attached a picture of where more or less this drain hole is located. It's just a small round hole about an inch wide with like a black rubber flap. Flap opens up from the pressure of the water and drains out. If clogged it WILL go inside your cabin. My first c43 never let water in the cabin as the car was in a nice city with no trees. My current c43 was most of its life in Chicago so got very very dirty..

Keep in mind this is not a picture of the c43 but same principle/location....
The green circle is where the hole is. The red circle shows the plastic shield you must remove to get to the passage and clean it out.

Not at all a hard job, remove screws unclip the shield and common sense will show you how to clean it out once the shield is off. Have a bucket of water or hose to clean it really good. This job is a MUST for this aged car, specially if you have never cleaned it out before.

 

Excellent call George Yup I've done mine after having learned the hard way with my old c240.... It gets very wet inside when the hole clogs up!!!

 

Picked up this time the correct part from the MB parts store using the correct part #
Now need to change into my work clothes and pop down into the workshop... See you all later.

 

Excellent, Thanks for sharing..

"ZAYED"

 

Last update for this thread and I can say that the job is done and the whine has disappeared.
I removed the passenger seat and that gave me plenty of room to lie on my back and get my head into the end of the foot-well and see what I was doing. The only small difficulty was getting the plastic lever clipped between the flap and actuator. Getting everything back together was straight forward and I also used the occasion to unscrew the seat back panel to reconnect the plastic vacuum hose which operates the side bolsters. Yes it had disconnected from the Y connector

A photo showing what's can be found behind the dash looking through the glove compartment opening. The coloured tubes are the different vacuum lines running to different actuators in the HEVAC unit.

 

I'm trying to fix the same problem in my clk55. The whine only happens when the ac wants to run, quiet if the heat is on. I put it off all winter, but it's getting hot now. I'm not sure which actuator it is, so I will be doing the under dash crawl to find it.
Thank you for posting the symptoms and solution.

 

I hope it's not the transmission torque converter like this guy!
https://mbworld.org/forums/glk-class...n-driving.html

 

Thankfully it's not transmission noise on my car. It's obviously one of the vacuum actuators. The noise goes away if I turn off the hvac. I just need to track down the culprit.

 

Excellent write up! I know its been a few months on this but I am having an issue with my footwell vents not opening. I changed the same actuator that you mentioned in your thread but they still appear to be closed.

Do you recall if there is a matching actuator on the driver side as well? Should they be changed in pairs? Any help on this matter would be greatly appreciated.

Thanks again

 

I'm not sure. Let me check the diagram and I'll get back later....

 

Awesome, thanks!

 

OK, if you go read post #36 in this thread (https://mbworld.org/forums/c36-amg-c...ml#post6969849), you will see a diagram as an attachment to the post.

Look closely at actuator #39 as it's the one which does the floor flaps (both sides).

 

Right, i saw that and that's the one i had replaced both the flaps still aren't opening. Just the floor flaps only. Do i need to reset the climate control module or something?