W124 Heater matrix problem - How can I tell if the heater ma

[Anonymous]

I am having a long running battle to sort my heating system out, have changed controller and duo valves and am convinced its not an electrical problem.

My problem is that the passenger side won't go cool. Drivers side seems ok.  

How would i tell if the heater matrix itself was the problem? What are the symptoms of a faulty one.
Is the duo valve on the inflow or outflow to the matrix (I think its the outflow , can anyone confirm)?

Its seems a big job to remove the dash and get at it so I need to be sure its the problem before I get it changed.  

I am running out of time before warmer weather makes my car unbearable, so any advice very welcome.

Keith
E300D  1996

 

[Anonymous]

W124 Heater matrix problem

The matrix is doing what it should and radiating heat. The matrix can only be hot if water is passing through it.  
The duo-valve must be passing water even when it should be off.  I'm not sure but doesn't an energised valve cut the water supply? Check there is actually 12v accross the valve.  Try swapping the connections from the other valve.
Ensure the air-con is switched off otherwise it will call for heat to re-heat the chilled air even if the chiller is not working, thus giving heat.

Will

 

[Anonymous]

W124 Heater matrix problem

Will
thanks but have checked all voltages. A/C is also off.  When dials are set for cold there is 0v on each valve, same both sides yet one side stays warm.  

I have tried a replacement valve but no difference so extremely doubtful that valve is at fault , unless I got a faulty replacement with exactly same fault.

 

[Andy]

W124 Heater matrix problem

Keith

If your still having problems. Then get it into someone who knows. Then think two or three times before tackling a heater matrix on a 124. With little experience and not having another car or manuals to guide you.
Then your a braver man than me. And still no gurantees that it will cure the problem.

Regards

Andy @ www.mercedeservicing.com

 

[Frazer]

W124 Heater matrix problem

I also have had a battle with my heating/aircon. I've had my '94 E280 for about 4 years. I've lost track of the number of times the aircon has been regassed (seems to disappear after about 6 months) but no leak can be found and numerous parts have been replaced.

However, my new problem is that the heater will not go cool on the drivers side (it will maybe 1 in 20 times you try). I'm going to try and solve the problem myself and wonder if anyone can can give me a head start. Where should I look first? I was keeping my fingers crossed that it may be the heater dial/switch itself just not responsing reliably to me turning it?


I've seen the duo valves mentioned although this thread would suggest something else may be to blame. If these are the culprit can anyone give me some details on how to replace, cost, complexity of work, etc

Any help would be greatly appreciated!

 

[Andy]

W124 Heater matrix problem

Hi Frazer.

With regards to the AC system. Did they fit UV dye to it?

Regards
Andy @ www.mercedesservicing.com

 

[Frazer]

W124 Heater matrix problem

Thanks for your reply Andy, hoped I might hear from you.

My dealer never did. But the last time I had it done I went to an aircon specialist who did put dye in (don't think it was u/v as could see it with naked eye - yellow stuff). Now its time to go back so they can see where the dye is but I have to say I can't see anything in the engine bay.

Trouble is I don't want to have the aircon looked at again until the heater problem is sorted - possible link? Will the aircon work (once regassed) if I can't even get cold air from the driver side?

BTW, is it worth buying the Haynes W124 85-93 manual? I guess its got to be pretty close to my car in most areas.

Regards

 

[Andy]

W124 Heater matrix problem

Hi Fraser

If there is no signs of leakage in the engine bay. I would look under neath the vehicle  over the gear box where the drain is. See if the evaporator is leaking.


Regards

Andy @ www.mercedesservicing.com

 

[Frazer]

W124 Heater matrix problem

Hi Andy

I'll have another look round for dye (BTW have had a new evaporator, condenser, air dryer, various pipes, etc). But I think I'll have to let my local aircon specialist have another look. Trouble is I don't want to take it to them while the heater is not working.

My priority at the moment is trying to sort the heater 'cos driving the car can be a pain with hot air that I can't stop. I saw on the one of the other threads that you suspected a sticky duo valve was causing a similar problem.

Hope this isn't a stupid question (up until now I've let my delaer do all the work on my car) but where is the duo valve? How can I test/replace it?  An easy job/cheap job?

I have a German & Swedish store on my door step, I might walk over later to see if they sell them.

Any further advice most welcome.

Thanks

 

[Andy]

W124 Heater matrix problem

Hi Fraser,

You have had nearly all the AC replaced. Did they replace the evaporator. Removing the dash to carry out the job? How long ago. Are you sure they havn't put it back together correctly or has the problem occured later on?

Regards

Andy@ www.mercedesservicing.com

 

[Frazer]

W124 Heater matrix problem

Problem is want and need to get this heater problem sorted out first. Bought '83-'93 Haynes manual yesterday evening to see if I can clue myslef up about these duo valves; haven't had a chance to read it yet. Does my "hot air only" problem sound like a duo valve? Do you have any advice (cost/difficulty, etc)?

The evaporator was replaced June '99. Don't know if the dash was removed. System worked after that (always does after a regas) but of course after a while, some months, it stops. Once heater sorted, sounds like I need to continue with tracing the leak either on my own or with my local aircon company.

Thanks again Andy

Regards

 

[Andy]

W124 Heater matrix problem

Hi Frazer

It could be either. You need to carry out the tests the system. Presumably written in the Haynes manual you have. You could try removing the top of the heater valve & check the rubbers and make sure they are free in their respective housings.

Regards

Andy @ www.mercedesservicing.com

 

[Anonymous]

W124 Heater matrix problem

Hi Frazer
I have many battle scars from this heater problem and the car is finally on its way to Andy in B'ham next weekeend.

However I can tell you what i tried.  Firstly the duo valve is near the o/s bonnet hinge.  Cost is around £80 takes less than 1 hour to change.  Its the thing everyone goes for first.  IN my case fitted new one no luck (unless new one also busted - unlikely).  The only other element to the system which is the second thing the experts go for is the heater control unit behind teh heater control valves.  Again less than 1 hours work but this time costs £200+.  I mangaged to get a used on from a breakers for £70 but in my case still no luck (unless this also was busted).  I'm in despair now that weathers warming up my passengers complain that I should go back to a volvo!  All my hopes are pinned on Andy now!!!!

 

[Frazer]

W124 Heater matrix problem

Andy and Keith,

Thanks for the info. Will get my hands dirty and let you know how I get on. No doubt I'll find more questions than answers so I'll be in touch......

Frazer

 

[Frazer]

W124 Heater matrix problem

You won't believe this guys but I haven't done anything and the system is working!

Keeping my fingers crossed.

Thanks again for the help.

Frazer

 

[Haig Tyler]

W124 Heater matrix problem

I had eratic heating caused by a faulty auxilliary water pump (electric pump just beneath the washer bottle).  I know it would seem not to be the problem here, but it would certainly be worth checking that it spins up when the ignition is switched on.  My did when I hit it, and continued working for 3 days before failing again.

They other related problem was caused by the internal temp sensor coming detached (it's in the housing next to the sunroof switch).  With it reseated, and the aux pump running the heating worked fine.

The Haynes manual doesn't seem to understand the W124 heating as the description doesn't mention the duavalves at all, and there's no picture of them.

Good luck

 

[thebeard]

There are three sensors one in the roof and two in the fan enclosure one LH and one RH. if one of the LH or RH become disconnected then that side will only give out full heat. the one in the roof interior light cluster will also give strange behaviour.

Below is a copy of my fix sent to Keith.

I have finally fixed the problem with the heater !!!!!!! Hurrah after checking the duo valve swapping around the connecter and swapping the control unit as you did.

The solution was to reconnect the RH matrix sensor cable which had somehow became disconnected !! My intention was to check that is was working correctly but when I looked it wasn't even connected.

If you want to check yours it's behind the control unit you will need to remove the control unit and the switch panel above ( this was a bit awkward I did it by removing the LH switch which top and the rear cable cover which you will need to remove by flipping it over) then push the switch panel back until it unclips then move it left behind the clip and it will the come forward and hang to the left.

The sensor is almost directly behind where the RH heater control dial sits " you know the one which directs the air up or down etc. "

It is inserted into the plastic housing for the heater matrix. and the connector is a push fit there is also one for the LH side.

I hope yours is just disconnected as was mine though I can't understand how this could have happened maybe it was not pushed fully in from the factory and 11 years later it fell out weird.

If mine had been connected I would have checked to see if it gave the correct readings i.e. compared the resistance with the LH sensor. at the same room temperature.