E280 (W124) Auto Est (96) Heating (duo valve)

[JensH]

I mentioned that I was a little unhappy with my heating, and with tell-tale constant warm air from the dash side vents, and after a bit of research, I have checked the duo valve and adjacent pump.
With ignition on, there is vibration from the pump so that seems ok, but NO "clicking" from the duo valve solenoids if the power supply is interrupted and reconnected, indicating that the valves are clogged, I believe.
Before I seek out a recon duo valve, has anyone had success in disassembling, cleaning and reassembling the duo valve unit?
I seem to be facing one thing after another at the moment, but I am hoping that it is just a case of progressive attention to odd bits of cumulative neglect, in what is otherwise a nice car and that at some point it will settle down to routine stuff, oil and tyres, vacuuming furry dice etc...

 

[television]

Before you start thinking about the duo valve is the engine getting up to 87°c .

There are a few different ways to check these duo valves, the 3 pin connector has a center pin live plus 12v, each outer pin is for each of the 2 valves. There should be 0 to 12 volt on the valve depending on the setting in the control panel, max heat =12volt.

This voltage is a pulsed voltage, it has to be as a straight voltage would just open the valve fully and nothing in between.

You have the main hose going in from the engine, this one should feel hot, you have 2 pipes coming out to the heater in the car. on max heat these two pipes should feel as warm as the ingoing one.

If the valve is good and working you can feel the pulses on the outlet pipes.

What happens to the valves or can happen is over the years the rubber seals in the solenoids can swell, this limits the opening of the valve.

It is never the floating valves in the ends of the solenoid that stick.

You can put a screwdriver handle to your ear and the blade on each solenoid and hear them working.

Before you replace the valve remove the 3 pin plug and with a 12 volt supply from the battery apply this voltage to the center pin and each outside pin in turn and that valve should make a healthy clonk, if it just makes a dull thud then repeat this a few time and it can help to free the solenoid up to increase its range of travel.

If the pipes leaving the duo valve are hot, then feel the other end of the pipes where they pass through the firewall to see if they are hot there, if much cooler then the heater matrix could be blocked.

 

[kth286]

they normally fail in the HOT position, which is ok in winter of course, but not in summer.

So a good design from that point of view.

 

[television]

they normally fail in the HOT position, which is ok in winter of course, but not in summer.

So a good design from that point of view.

Hello David, I do not know where that saying that they failed in the hot mode came from, indeed I posted the same before I fully dismantled one, the solenoid plunger is spring loaded to keep the valve closed, therefore any failure the must fail in the cold mode except when the rubbers are too swollen to enable the core to close fully,,, it is the voltage applied that keeps them open.

 

[balge59]

Yes, did the duovalve on my300TD, just cleaned it up and it works fine now. Any number of DIYs on the web.
cheers

 

[JensH]

Duo valve

Before you start thinking about the duo valve is the engine getting up to 87°c .

There are a few different ways to check these duo valves, the 3 pin connector has a center pin live plus 12v, each outer pin is for each of the 2 valves. There should be 0 to 12 volt on the valve depending on the setting in the control panel, max heat =12volt.

This voltage is a pulsed voltage, it has to be as a straight voltage would just open the valve fully and nothing in between.

You have the main hose going in from the engine, this one should feel hot, you have 2 pipes coming out to the heater in the car. on max heat these two pipes should feel as warm as the ingoing one.

If the valve is good and working you can feel the pulses on the outlet pipes.

What happens to the valves or can happen is over the years the rubber seals in the solenoids can swell, this limits the opening of the valve.

It is never the floating valves in the ends of the solenoid that stick.

You can put a screwdriver handle to your ear and the blade on each solenoid and hear them working.

Before you replace the valve remove the 3 pin plug and with a 12 volt supply from the battery apply this voltage to the center pin and each outside pin in turn and that valve should make a healthy clonk, if it just makes a dull thud then repeat this a few time and it can help to free the solenoid up to increase its range of travel.

If the pipes leaving the duo valve are hot, then feel the other end of the pipes where they pass through the firewall to see if they are hot there, if much cooler then the heater matrix could be blocked.

Great stuff Malcolm, thank you - I'll follow these guidelines.

As it happens, on a 130 mile drive down this morning, the vents did all blow cold on the coldest setting (before the click off), so maybe it's an intermittent problem? I'll have a look at the weekend...

MB dealer current quote for a new duo valve btw is £344.40 incl. VAT.

Jens

 

[kth286]

Hello David, I do not know where that saying that they failed in the hot mode came from, indeed I posted the same before I fully dismantled one, the solenoid plunger is spring loaded to keep the valve closed, therefore any failure the must fail in the cold mode except when the rubbers are too swollen to enable the core to close fully,,, it is the voltage applied that keeps them open.

Have a look at the water circuit via your reference files - titled : Operation of engine off cooling - 20-0060.

 

[television]

Have a look at the water circuit via your reference files - titled : Operation of engine off cooling - 20-0060.

David these valves are spring loaded to stay in the closed mode, if you read 20-0060 operation of engine cooling it says the duo valves must be closed to force it into the bypass loop. You can only get it into the closed mode by controls at the coldest point or remove the plug on the valve.

If you want to use the rest function the temp controls have to be set at the desired temps, this opens the valves.

Therefore if the voltage is removed from the duo valve it will be in the closed mode natural state, the solenoid can only move one way and that is up to open the valve.

 

[JensH]

?????

David these valves are spring loaded to stay in the closed mode, if you read 20-0060 operation of engine cooling it says the duo valves must be closed to force it into the bypass loop. You can only get it into the closed mode by controls at the coldest point or remove the plug on the valve.

If you want to use the rest function the temp controls have to be set at the desired temps, this opens the valves.

Therefore if the voltage is removed from the duo valve it will be in the closed mode natural state, the solenoid can only move one way and that is up to open the valve.

Lads, this is all going a bit over my head...

 

[television]

The 124 duo valve is much simpler than some in other models.
For the valve to be open for max heat it must have near on 12volt on the coil.

They are simple to take apart, 5 screws hold the top coils on and it lifts off, care must be taken so that nothing drops out, there is the piston with a spring under it and a little bronze valve in the bottom, these are delicate, so take care, there are a couple of Utubes out there.

 

[JensH]

The 124 duo valve is much simpler than some in other models.
For the valve to be open for max heat it must have near on 12volt on the coil.

They are simple to take apart, 5 screws hold the top coils on and it lifts off, care must be taken so that nothing drops out, there is the piston with a spring under it and a little bronze valve in the bottom, these are delicate, so take care, there are a couple of Utubes out there.

Wilco.

I'll update you after the week-end to tell you about all the little bits that I have lost!

 

[television]

Magnetize the screwdriver tip by stroking the tip over a magnet

 

[kth286]

David these valves are spring loaded to stay in the closed mode, if you read 20-0060 operation of engine cooling it says the duo valves must be closed to force it into the bypass loop. You can only get it into the closed mode by controls at the coldest point or remove the plug on the valve.

If you want to use the rest function the temp controls have to be set at the desired temps, this opens the valves.

Therefore if the voltage is removed from the duo valve it will be in the closed mode natural state, the solenoid can only move one way and that is up to open the valve.

"...........voltage removed from duo valve it will be in the closed mode"

agreed, which means that full heat will be ON in the cabin.

So, they normally fail in the hot position.

 

[television]

"...........voltage removed from duo valve it will be in the closed mode"

agreed, which means that full heat will be ON in the cabin.

So, they normally fail in the hot position.

If it is closed no water goes through it and the heater matrix will be cold.

Please tell me how you can get full heat when the valve is closed, when the valve is closed it forces the bypass into operation.

 

[JensH]

W124 E280 Auto (Est), Heating (cont'd)

Latest on my heating:

Dismantled, cleaned (it wasn't that dirty) and re-assembled duo-valve. I wouldn't say that the motion of the plungers was that smooth, though - so perhaps they are worn?

There still seems to me to be something eccentric about my heating system, like someone has tinkered with it in the past and got something wrong somewhere.

For example:

* I consistently get warm air out of the centre vents, with the AC off, and this generally feels about the same as the air coming out of the side vents;
* I wouldn't say I ever feel really fresh air coming through the centre vents - I thought this is all they do when AC is off - my manual says that they do feed warm air when AC is on;
* When I test the AC it doesn't really seem to do its chilling job. It is not cold enough - this is surprising because the AC was overhauled by a specialist garage (Prestige, St Albans) less than 2 years ago;
* I still don't think that the system is that hot on the hottest setting. I can always comfortably hold my hand in front of a vent.

Having said that the car is generally comfortable, so maybe it is me not understanding the system properly and it is just idiosyncratic?

Autodeutsch in Camden checked out the heating on the last major job (exhaust) and said they thought it was ok. They also said that they thought heating was a weakness on W124s generally.

Seems to me that I have an issue, though, along with the cruise control, which is u/s, where I may actually be better off seeking help from a main dealer?

I do seem to be losing a bit of coolant btw (nothing I have not been able to trace to a leak and defnitely not from the duo-valve).

Jens

 

[nyx]

my 124 heating is amazing. super hot air within 30secs of starting from cold and if i turn it up to full the air vents are way too hot to hold my hand in front of them.
the centre vents always supply ambient temp air from outside.
maybe as mines an early car they changed something later on also i don't have ac

 

[balge59]

The plungers should move smoothly when cleaned up

W124 should not blow hot air out of the centre, a problem with the flaps?

http://mbworld.org/forums/e-class-w124/430593-center-vent-question.html

Heating is ok on both my W124s, certainly gets uncomfortable on full heat.

What temps do you get on the gauge, mine sit at around 85C and warm up fairly quickly.

Is it factory a/c or aftermarket?

 

[television]

I owe Kth286 an apology, the valves do fail in the hot mode, the plunger comes down under load to close it off, if a coil failed then it would be hot.

The exception, well not an exception as such is the 140 duo valve, the rubbers swell up preventing the valve from opening, there are no rubbers in the 124

So sorry David

 

[JensH]

I owe Kth286 an apology, the valves do fail in the hot mode, the plunger comes down under load to close it off, if a coil failed then it would be hot.

The exception, well not an exception as such is the 140 duo valve, the rubbers swell up preventing the valve from opening, there are no rubbers in the 124

So sorry David

Ah, Malcolm, that does suggest that I might try a replacement recon duo-valve, judging by my symptoms, unless there is a fix for the coils?

I reckon I could handle this. It's one (large) hose in and two smaller hoses out, isn't it? Anything more complicated than that, or elsewhere in the system, I'd need to leave to someone else... I'm a musician!

Thanks

Jens

 

[JensH]

The plungers should move smoothly when cleaned up

W124 should not blow hot air out of the centre, a problem with the flaps?

http://mbworld.org/forums/e-class-w124/430593-center-vent-question.html

Heating is ok on both my W124s, certainly gets uncomfortable on full heat.

What temps do you get on the gauge, mine sit at around 85C and warm up fairly quickly.

Is it factory a/c or aftermarket?

Hi, thanks for this and the link.

Mine is a late model, '95, registered '96, E280 Auto Estate (with very little rust, before you ask!). AC was factory-fitted - standard two zone heating with AC default on, unless 'EC' button engaged (with fan on, of course).

Temp gauge settles at around 87-88º and gets there in about 5-7 mins from a cold start. The temp and oil gauges are rock steady, as is the engine. I do seem to be losing coolant, though. Had to top it last week (1.5l MB), when the warning light came on - there was some leakage from doing the duo-valve, but there seems to be an ongoing loss of coolant somewhere... Now that I think about it, there is an occasional (very occasional) slight smell of coolant in the cabin...

Cheers,


Jens