w124 twin air climate control help needed

[e36bob]

My 1989 W124 estate is fitted with dual air con.
The control unit has dual temperature thumbwheels, air flow direction and blower turn switches inside those, and three vertical switches in the centre of the panel.
My unit will not control the air temperature on either side, and is stuck on hot.
When the air con switch is pressed, nothing appears to happen, but the recirculation air works. This is the only way I can cool the cabin.
The air direction dial works fine, as does the blower fan, although slightly noisy.
The left hand thumbwheel has a broken output shaft going into the rheostat on the circuit board.
I am trying to find a replacement control panel to see if that works.
According to haines, my system is from Valeo.
Does anyone know where the dual cabin air temperature sensors are fitted?
Haines only gives the unit fitted to the interior cabin light unit, I presume this is for the mono system only.
Where are the relays situated?
I have seen similiar dual controls on the 300 and 500 series.but finding a reasonably cheap unit is proving difficult. mercedes quote 350+ ouch!!!

Thanks for any advice.
Bob

 

[jberks]

I have never seen a merc system that was anything other than dual (going back to 1979). What you describe sounds to me like the standard Merc system that was pretty much unchanged until they went digital recently. The sensor is in the overhead panel as per the haynes. Check the duovalve too, a very common failure.

 

[e36bob]

dual air con problems

Thanks j, for your reply.
The reason I stated a dual unit is because my wife has an E36 124 model, and there is only one heat temperature thumbwheel .
I managed to get a dual control unit from breakers in reading.
I fiitted it hoping all would be well, but I am still only part of the way there.
If I press the central air control switch, the power light on the switch does not light up, but I can hear the left hand unit click, and then it controls via the thumbwheel, but the right still does not respond .
If there is relay for both sides , I might swap them around.
If I press the air con switch again, I only get hot air from both sides, no doubt due to the system requiring regassing.
I found the duo valve, it looks to have two hot feeds to it, is this correct?

Thanks again for your reply.
Bob

 

[macca2210]

Hi,

I recently had to replace my Duovalve unit, but had some weird symptoms which seemed more electrical than actuator based.

This site has some useful information on the cooling/heating system:

http://www.mercedesshop.com/diy_stevebfl_0.htm

From memory, there are a number of small tubes running from around the cabin, to a temp sensor behind the glovebox. It has a small fan sucking air over the temp sensors. If the car has swollowed a lit of dust over its life, the intake to the tumes can get blocked.

Also, there are vacuum driven air baffles to control heat & cool air. It is possible that a baffle is stuck or has lost suction. This would be a mother of a job to get to.

I've also read that when the temp control pots get dirty/old/scratchy that the controls go heywire. Probably the next place to look if you have already replaced the Duovalve.

There are a number of good articles on this site on climate control probs...

Hope that helps a bit.

 

[e36bob]

w124 air con problems

Hi macca,
Thanks for your reply, I shall check the intake tubes as you suggested, the car had lots of leaves ( and acorns!) in the engine bay water channels .
Where is the temp control pot you mentioned?.
I shall also check that the duo valve is getting a signal from the each controller .
I can see myself having to remove the dash at some stage to access the system, so some light reading from haines is in order.
Thanks again for all replies.

 

[Keith]

try the air sensor suction fan

I had similar problem and after replacing both control panel and duo valve at a cost of £750 inc labour , discovered myself that neither was at fault. It was the tiny fan behind the near side vent that sucks the air across the roof sensor via a tube. This tiny fan had failed so that the roof sensor was not reading correctly. The fan cost about £25 to replace and took about 20 mins.

I hope you check this before the more expensive items.

Incidently if anyone wants a duo for a 1995 E300D then I have a perfectly good one for sale. I might have the controller board in the garage somewhere also.

hope this helps

 

[macca2210]

Hi macca,
Thanks for your reply, I shall check the intake tubes as you suggested, the car had lots of leaves ( and acorns!) in the engine bay water channels .
Where is the temp control pot you mentioned?.
I shall also check that the duo valve is getting a signal from the each controller .
I can see myself having to remove the dash at some stage to access the system, so some light reading from haines is in order.
Thanks again for all replies.

Hi,
By "temp control pot" I meant the temperature control thumb wheel in the cabin.

Refer to a forum thread "W124 heater and aircon puzzle" which has a reference to photos of removing the control panel inside the car.

Also, this forum thread has some useful diagnostic advice - " How to save £750 with 2 squirts of WD40 - My W124 £750 heate"

Good luck...

 

[e36bob]

w124 twin air con problems

Keith,
thanks for your reply, how do you access the fan you mentioned?
Thanks in advance.
Bob

 

[Keith]

accessing the temp sensor fan

just remembered you can test it without removing, here's how:
- remove roof air sensor assembly from the rubber pipe attached to it
- get a small piece of paper about the size of a postage stamp and hold it over the end of the rubber pipe.
- turn on ignition
- release paper (if there is suction so it sticks to pipe then the fan is not the problem, if it falls off then the fan is not working so proceed to replace)

instruction for replacing:
- remove glove box or passenger airbag depending which you have.
- remove nearside air vent
you will find the fan which is about 2 inch diameter and dangling on the end of a piece of rubber pipe right near the back of the air vent.
- pull of the electrical connector and the rubber pipe to retrieve the fan.
- replace in reverse.

the good news is it only cost about £25 from the merc dealer (the cheapest spare I ever bought from them!).

This sorted out my uncontrollable cabin temp but not before I had wasted lots of money on duo valve and electronic controller (as recommended by the merc dealer blockheads). They didnt even know of the existance of the suction fan.

hope this solves the problem for you, if you do decided you need a duo valve come back to me as I have a new spare (I put the old one back in as it wasnt bust).

Keith

 

[e36bob]

w124 dual air con problems

Keith,
thanks for your reply, I shall follow your instructions, and see what happens.
Thanks again to all who have contributed.

 

[e36bob]

w124 dual air con problem Success!!!!

Thanks to all for your replies.
Problem now sorted!!!!
macca 2210
Keith
jberks.
The consensus of opinion you guys gave were spot on.
The air pipe to the temperature sensor in the cabin light control panel was full of crud.
The right hand cabin duo valve was stuck.
Freed off with a tap, and hey, individual temp control on both sides. even the air con gets cold too!
Once again, thanks to you guys, you have saved me a fortune..
Keith, you mentioned you had a spare duo valve.
If you still have one, I would like to buy it.
Do you have a spare water pump for the system?
Please let me know.