How to save £750 with 2 squirts of WD40 - My W124 £750 heate

[Keith]

Some will remember my saga trying to get my heater back under control.  this started with hot air blasts after engine warm up over six months ago (previously cabin temp had been maintained beautifully in all circumstances without intervention) and ended with being unable to get rid of heat or control it properly.

I have used 2 highly experienced merc trained independents (identities protected as I know they have A1 reputations generally and have tried their best).  Along the way they have tested every wire, replaced duo valve and heater controller (thankfully with a salvaged part otherwise bill would have been higher).  Result bill total of £750 problem not solved.

A member of this forum (can't remember who - have lost my previous posts , but many thanks anyway) suggested using cleaning fluid on the control potentiometers attached to the heater dials.  I didn't have any cleaning fluid so tried WD40 - result problem solved controls work again cabin temp maintained perfectly.  

For info this is a '96 W124  300D with factory air fitted.

Experts please note this one and save your customers the same financial pain as I went through.

 

[G4VSQ]

How to save £750 with 2 squirts of WD40

A word of (slight) caution. WD40 is not particularly good for potentiometers, and can cause more problems in the long run.

The best substance to use to clean a noisy/dirty pot is a proprietary switch cleaner, such as De-Oxit or RS brand. Make SURE if you buy switch cleaner it is the cleaner PLUS lubricant. And repeat the treatment regularly.

Switch cleaner/lubricant is available from Maplin or I can supply it (I'm a radio engineer and also restore vintage radios, so I have quite a lot of it!)

Well done on the simple fix-I guess the way to tackle any job is start simple!

Al
Mercedes 260E money pit

 

[Neil Williamson]

How to save £750 with 2 squirts of WD40

Hello Keith

Can I just ask exactly what your problems were?

My E320 with FF A/C seems to have a will of its own with regard to temperature maintainance. When the car is started from cold, irrespective of the position of the controllers, I get warm air. Much fiddling yields chilled air but there seems to be little control between Freeze and Bake!
Additionally, can anyone  tell me what the dot position indicates on the temperature controls? Is this an off position or a maximum cooling? There seems to be a detent on the switch which clicks when this point is reached.

Many Thanks

 

[Keith]

How to save £750 with 2 squirts of WD40

Neil
my problem was identical to the way you describe yours, except that when I had the car for the first 12 months it was perfect , then the trouble began last november with too much warm air and progressed to be exactly like you describe.  Much fiddling yielding either hot or freezing and nothing in between.  

I almost gave up hope and was toying with getting rid of the car until WD40 came to my rescue.  Pity I did not try it before sh*ll
ing £750.  

Al is quite right that WD 40 is not ideal and an electical cleaner with lubricant is the correct thing.  Still its not the first time I used WD40 on electricals and seemed to get away with it by being applying a tiny amount direct into the hole in the potentiometer moulding.  I think it only causes probs on unisulated parts , most PCBs are laquered for insulation / moisture protection.

Let us know how it goes.

Keith

 

[AndyH]

How to save £750 with 2 squirts of WD40

Could this problem be the same as that I have just found in my 1989 300E? It is either cold through the centre vents only, or full hot through the side vents, screen and foot-well. The a/c was fitted by the dealer (through B.K. Thomas) not from the factory.

 

[G4VSQ]

How to save £750 with 2 squirts of WD40

The problem with WD40 is that it can sometimes cause the carbon track in the pot to disintegrate, and this can cause worse problems than before as the track will actually wear away. The pot will eventually stop working properly.

This doesn't happen in all cases of course but you are still best off with a proper switch cleaner/lubricant, which will have a much longer lasting effect anyway, as it is depositing a fairly stable lubricant.

Cheers,
Al

 

[Keith]

How to save £750 with 2 squirts of WD40

AndyH

I understand that dealer fitted a/c and older factory a/c can operate as you describe, also fresh or cold air only through centre vents.  I was told that only more recent fact a/c on 124 has fully integrated air through all ports.

Maybe someone more knowledgable will confirm.

Keith

 

[Andy]

How to save £750 with 2 squirts of WD40

Hi all,

Only the last of the facelift 124's have hot and cold air coming through the centre air vent. 1988 vehicle would definately have just cold air coming through the center air vent.

Regards

Andy @ www.mercedesservicing.com

 

[Neil Williamson]

How to save £750 with 2 squirts of WD40

I would still like to know what the dots signify on the temperature wheels!!!

 

[john lang]

Heater potentiometers

Hi
I've got the very same problem on my 200E. The drivers side temp control doesn't work and it's on hot all the time unless I give it a wiggle.
Does anyone know how you get to the potentiometer to clean and lubricate the track ?
Thanks
John

 

[Jim Gallagher]

Central Air Vents

Hi,
I have a 1994 E220,W124, I only get cold air through central air vents on the dash.

 

[joe bloggs]

Hi Guys,
Couple of things to check before attacking your pots, firstly the duovalve on 124/126/129's etc is either on or off with no inbetween, control unit either feeds or does'nt feed the valve, therfore if you put your hand at the heater outlet you can feel it heating and cooling, may get quite cold at times even if temp wheels are on warm. depends on interior temp, overall temp should be as selected.
Also check the sensor at the interior llamp, this has a small pump below the glovebox connected via a rubber tube to draw air into the sensor. with the ignition on stick a bit of tissue paper over the sensor grill, it should stay there and fall off when the ignition is turned off.
Next thing is the two sensors clipped into the heater box (behind radio) these can get knocked out when radio fitting or any other fiddling around in this area.
If the heater is fully hot regardless of settings then as the duovalve opens on no current check the power supply to the ecu and the valve, centre connection to valve is ignition supply (same fuse as ecu), control unit earths the outer pins when it wants cold air (easy to check valve with 2 bits of wire)
Check resistance of valve also, compare sides (middle left and middle right) as the resistance has been known to reduce and therfore draw more current through the ecu, this has a failsafe and will switch off if too much current is consumed by valve (heater then on full hot).
The detents on the temp wheels do not operate any switches, they are just a mechanical guide for full hot/cold, max/min resistance fed to ecu

Regards
a Merc. Tech.

 

[GaryC]

Hello,

Yes, the Duo valve was just a electrial magnetic valve, which control whether there are hot water flow into the heater matrix or not, not a varible valve like the water tap! Two of them stick together, in which each one control the temperature of each side.

For mind, if it is operating, it wil have some pluse 'click' in a period of time when it open and close, depend on the temperature setting and interial temperature, so may be is a good point to check whether it is work or not.

For the temperature sensor which stick on the roof, (beside the lamp), there was a rubble hose connected to it, and the other end was that air pump, please make sure that the hose was connected with the sensor, as it was easily come of, when u replace the light bulb.

A I remember so far, last time when I discover the problem of my heater form the temperature selection, I use the wiring diagram and almost chase every single part of the heater system, even I have de-commission and clean the duo valve and also the re-circulating pump, and check every sensor and air pump, to make sure their work.

Finally no hope, but I discover, if I brifely turn the temperature control knob up and down for few time, it will improve! amazingly cold air arrive!! the I notice is the problem of the potential meter...... after cleaning it with contact cleaner, then it work prefectly again

This give me huge hassle to check everything, but save me a lot of money....

 

[Malcolm Brown]

Hi, I know this sounds really picky but...

The detents on the temp wheels do not operate any switches, they are just a mechanical guide for full hot/cold, max/min resistance fed to ecu

On the 126 (switch part no 126 820 (left, or 830 for right) 0103 , the detent at the minimum position is a switch.

But there's some really useful stuff in this thread. Thanks, guys.

 

[steve moores 1]

Only the last of the facelift 124's have hot and cold air coming through the centre air vent. 1988 vehicle would definately have just cold air coming through the center air vent.[/quote]


I am just in the process of buying a late '95 E220 C. Should this come with hot and cold thru the centre air vent? :?