Unregulated internal heater - phew!!

[steveb]

I have a problem with the internal heater on 560SEC - it seems to be on full heat at all dial positions except Min, both sides.

Any ideas for the fault - I have scanned the newsgroups & the monovalve crops up freqently, but usually in the context of NO heat.

Fortunately I live in UK, so am usually untroubled by external temperatures much above a 'disagreeable chill'.

Thanks

Steve

 

[lindowkid]

I has a similar problem, but in the Summer was a bit hot! It turned out to be small microswitches that turn off the heater at the bottom of the sliding heater switches. Don't know if this is the case on yours. Also its worth knowing (because I wouldn't have guessed) that the heater slide has to be all the way down and enguage the micro switch irrespective of whether the fan is switched off to stop it pouring hot air through.
To be honest I still have difficult regulating the temp in my car it seems all or nothing.
Andy

 

[Francois]

In these cars there are a whole host of things that can cause this.

lindowkid touched on one of the problems, the other more common problems are the following:

1. The pots in the temp switches are busted and needs replacing.
(This is ussually the case when you have irregular heating/cooling.)

2. The temp sensor above the rear view mirror is nor working properly.

3. The duo valve (US models have mono valve) is busted.
(This will cause hot water to always be circulated through the heater matrix and hot air will always enter the car.)

Hope this helps.

 

[Keith]

Heater pots?

Francois
was interested in your reply I have had long running 2 year saga trying to tame my heater in a 1995 W124. Have replaced duo valve , all 3 sensors and even put in a reclaimed controller unit.

I never thought of the heater pots since there are two of them and the problems I am having seemed to affect both sides. do you still think it could be the pots? if so can they be cleaned or must they be renewed?

Your expert view would be appreciated

Keith

 

[Francois]

Keith,

I have not had personal experience with the pots in the temp controls, but the arguments is as follows:

If the potentiometers in the tempreture controls are shot, then the incorrect voltage is sent to the computer and the computer will think that you would like a warm car. Thus it only pumps in hot air.

From what I could tell from other people, it is easier to go to a scrap yard and try to find a match for the controller wheels on your car and then just replace them. I don't know much about the W124 cluster, but I am sure that if you can find your way to the control wheels it should not be a try and open the pots and clean them. I would warn against using WD40 since it seems to damage the carbon in the pots.

That is unfortunately all I can tell you about the control wheels/pots. Something else to check could be the circulation pump of the tempreture sensors. Sometime you replace the sensor with a new one but the line to the air pump from the sensor has a leak or the pump does not function. This cause the sensor to register an incorrect temperature. (Not sure how this works on the w124)

Hope this helps a bit...

 

[Keith]

circ pump

Francois
thanks yes I had a 'feeling' I should investigate the air circ pump, will look at that first then the pots
K

 

[Keith]

air circ aux fan - seems to be my problem

Francois I pulled out the cabin temp sensor and let it dangle from the roof lining just to give it free air in case the circ fan had stopped working .

Guess what - my wife (who drives the car most days and is its biggest critic) says that it has behaved perfectly today with both dials not needing to be touched just left on white - just like when we first got the car.

I have had severe temperature control problems for 18 months , changed various components with no real success and quite a bit of expenditure. I think you have pointed me at the cause which at least 2 merc trained specialists have missed so thank you very much

I only realised the existance of this fan when I had the airbag out a few weeks ago and judging by the lack of success that others have had in diagnosing my problem it seems there is a general ignorance about its existance. I will now seek to remove it at the weekend , test and get a replacement.

Just wonder if this is the cause of the original problem which started this thread. Its so easy to check for it too.

Keith

 

[Francois]

Keith,

I certainly hope that this is the cause and that it could be rectified now.

There are such a lot things that can go wrong, that you never know where to look first.

If I recall correctly, it was either Talbir or Andy that first told me about this little pump and the anoying results after it stops working. It could also be that you straightened out a kink somewhere when you left the sensor dangling...