Heating Problems 1995 124 E300D Duo Valve?

[Tony Foran]

Duo valve problems (Please excuse but this I posted in error initially to "Favourites" thread)

Hi all,

I have heating problems that I suspect it may be duo valve problems on my 1995 124 E300 diesel. This model does not have the air-conditioning. Contrary to most of the other threads that I have read my problem is that the unit delivers cold rather than hot air.

Experiences to date: firstly, the recycling motor was not working which I removed and found that it sometimes worked when tilted. On removing the brushes I found that these were loose so I cleaned and refitted and this unit then worked. This fixed the problems in the car for a few days but while the motor continues to run the car is now once again delivering cold air.

When I remove the duo valve and connect to the power supply the valves open and close (as required? - I have read somewhere that this is variable but mine appeared to open or close - no apparent middle ground!). However when I replace the unit in the car it still delivers cold air. When I remove the (removable) end pieces (valves?) the unit then will deliver hot air into the car but as there are no valves in place it is not possible to control the quantity of heat (other than by adjusting the fan speed).. On replacing these valves one of which I glued into position and the other which I cleaned to make sure that is totally free there is no difference -- the air delivered on both sides is still cold.

Has anybody had similar experiences? -- These symptoms seem to be at variance with most of the threads that I have read to date.

The symptoms suggest that there is a sensor somewhere that thinks that the interior is hot but then if so, why do the valves open and close when the unit is opened but still powered by the car's electrics?

Help!

...Tony

 

[fred_raven]

duo valve

hi - had similar problems on my 210 , took duo valve apart cleaned and all appeared to be working but still no heat on one side. did the swap pipes to ensure heat changed side , it did , took it apart again , but still appeared to be working! in the end bit the bullet and replaced it - problem solved! I hate spending money when things can be fixed but sometimes !!!!!

 

[Parrot of Doom]

The valve is designed to fail in the 'hot' position. If when out of the car the valves function normally, get a multimeter across the pins and measure the voltage output from the car. The centre pin will be common. I'd go and measure mine for you but its getting dark and its cold.

 

[Tony Foran]

Problem persists although electrics seem OK

Apologies for not getting back sooner, but the weather has been atrocious over here in Ireland last night and early this morning.

At lunchtime, I did as you suggested. The unit appears to work correctly in that when switched on with the internal settings to cold there is a full 12 - 13 V on either side and when the internal knobs are set to Maximum (defrost symbol) the voltage drops away to 0v (as you stated). Also, when the car was hot with the temperature setting midway internally, the voltage fluctuated obviously with the valves opening and closing (as one might expect to maintain a constant temperature inside). Therefore I do not suspect any problems with the internal controls (rheostats).

However, here the plot thickens!

As I mentioned yesterday I was running the unit with out the "valves" installed. I cleaned these perfectly and they move freely on the shafts. However, once I reinstalled these in the unit, I again have the same problem – no heat whatsoever on either side. The symptoms appear like there is insufficient “pressure” in the hoses coming to these valves to "lift them".

To summarise, the unit appears to work correctly both from the water heating and from the voltage perspective once these valves are not installed. However with the valves are in place I'm back my basic problem -- no hot air.

….Tony

 

[Ian B Walker]

You might have an air lock in your heater system. This would prevent the passage of hot water. Worth a look at anyway.

 

[Tony Foran]

Air Lock

Ian,

Perhaps so but does not explain why it always works when I remove the "valves" - I would have expected that if there was an air-lock that it would have been "removed" by now.

...Tony

 

[television]

Are you sure that the pump is running 140 in the link

http://www.detali.ru/cat/oem_mb2.as...GM=717.430&CT=F&cat=15S&SID=83&SGR=180&SGN=04

 

[Druk]

And another quick check is to hold a small piece if tissue against the small grille at the left side of the interior light. With the ignition on it should be held by the suction from the pump located below the glovebox. If the tissue falls then the pipe is off/grille choked/pump duff. The pump pulls air past a temp sensor to determine how hot/cold the car is inside.

 

[Tony Foran]

And another quick check is to hold a small piece if tissue against the small grille at the left side of the interior light. With the ignition on it should be held by the suction from the pump located below the glovebox. If the tissue falls then the pipe is off/grille choked/pump duff. The pump pulls air past a temp sensor to determine how hot/cold the car is inside.

Druk,

I'll try this - but it does not explain why the valves open and close a) when the unit is split or b) as I am getting open/shut/varying voltages with the unit in place. I am reasonably satisfied that the unit is getting power and that the "top part" of the valve is functioning properly.

...Tony

 

[Tony Foran]

Are you sure that the pump is running 140 in the link

http://www.detali.ru/cat/oem_mb2.as...GM=717.430&CT=F&cat=15S&SID=83&SGR=180&SGN=04

Malcolm,

Are there 2 pumps? Or on my model is this the pump that is part of the duo valve assembly? If so, this was my initial problem but I took pump apart, cleaned brushes and re-assembled. This unit now runs (and if I insert screwdriver in the outlet pipe (!!) I can sense the blades turning.

If this is the only pump in the system, I read somewhere that its only effect is when the car is stationary/(hot in traffic).

...Tony

 

[Tony Foran]

You might have an air lock in your heater system. This would prevent the passage of hot water. Worth a look at anyway.

Ian,

Re airlock: Do you know if there is a circulating pump other than the one that is part of the duo-valve assembly?

Also, I presume that the "rubber stub" (the on that is on the "top part" of the unit is some kind of "bleed" valve - however if I open/remove this I get a poor flow of water - is the entire system based on convection or should there be a "pressurised" exit of water at this point? If so, the lack of pressure would explain the "valves" not lifting on their shafts (but I am still baffled as to the efficiency/heat of the system with the "valves" removed!

 

[Tony Foran]

Photo of the "Offending" article

This is what it looks like re "pump" suggestions...

...Tony

 

[television]

There are some good links out there

http://v12uberalles.com/Rear_AC_System.htm

The best one is should be here but I cant find it, I am still looking, its the link that benzworld sends people to

http://pages.prodigy.net/jforgione/MB_DI.html

 

[LastMinute]

Are there 2 pumps?

No - on late 124s the pump is part of the duo valve assembly.

The Detali link Malcolm posted only applies to older 124s where the pump is separate from the duo valve. This is the link for yours.