4 zone Thermotronic problem

[Timmy M]

Hi People,
I have a 2004 E320 CDI with 4 zone Thermotronic. It has over the last couple of days developed a fault where the rear system is only pushing out hot air no matter what temperature you set but the front still works normally. oddly though the fault only occurs in hot weather as I had a late drive home last night and the system worked fine. I have had the system re-gassed any thoughts or advice would be appreciated

 

[christopherwk]

I also had the same problem, happened last summer in the hot weather. It was a faulty duo valve, about £25.

 

[Timmy M]

Thanks Christoperwk,

how much was it to fit?

 

[Diesel Benz]

I also had the same problem, happened last summer in the hot weather. It was a faulty duo valve, about £25.

Not actually a duo-valve but the more or less equivalent heat exchanger shutoff motor on a W211.

DIY instructions:
DIY: Installing a new Changeover/Heater Control Valve - MBWorld.org Forums

 

[Timmy M]

Thanks Guys,
I'm sure ther will be more questions but for now thanks again

 

[christopherwk]

Ah, actually looking at the invoice it's a "shut-off valve for heater core" - I hope that's right!

Total cost from main dealer was £567.25 + VAT

The part itself was around £25, but there was the labour, diagnostic checks, remove/install SBC?, deactivate/active SBC, and bleed brakes.

I don't understand what this has to do with the brakes though?!

 

[Diesel Benz]

Ah, actually looking at the invoice it's a "shut-off valve for heater core" - I hope that's right!

Workshop documents call it "heat exchanger shutoff motor". EPC calls it a "change-over valve". Your dealer billing system uses another name but all are reasonably well chosen.

 

[Timmy M]

That seems a totally different system to the A/C but your experience has certainly helped me and I am doing the job tomorrow... I will let you know how it goes

 

[Timmy M]

It was a faulty valve and it is something a qualified mechanic only should undertake as it involves disconnecting the brake pedal and moving some brake parts for access. However the Mercedes mechanic that did it for me, did it at my home and completed it in under an hour whilst the car was on the floor.. Incidentally Mercedes have sold over 1500 "duo-valves" in the last 12 months in the UK alone!!
Thanks for all the posts and hopefully this will help others

 

[christopherwk]

Glad it's sorted.

Does anyone know if this is common only on cars with 4-zone Thermotronic, or does it also affect cars with standard Thermatic only?

 

[Timmy M]

Not sure, but I think that MB squeezed every penny from you sorry to say. has your car had any other issues??

 

[Diesel Benz]

It was a faulty valve and it is something a qualified mechanic only should undertake as it involves disconnecting the brake pedal and moving some brake parts for access. However the Mercedes mechanic that did it for me, did it at my home and completed it in under an hour whilst the car was on the floor.. Incidentally Mercedes have sold over 1500 "duo-valves" in the last 12 months in the UK alone!!
Thanks for all the posts and hopefully this will help others

Now that sounds odd. The official workshop instructions do not suggest removal of the brake pedal (see AR8325P1140T). Also if you look at this DIY guide, it actually is a DIY job and many owners have completed the task.
DIY: Installing a new Changeover/Heater Control Valve - MBWorld.org Forums

I cannot remember the date the part was changed but obviously the new part should hold better. The 2-zone AC has a different valve part, not sure if those fail equally, there is a modified part anyway.

The issue with the 4-zone system is that the valve gets stuck and either you do not get warm air at cold outside temperature (valve stuck closed) or at very hot ambient temperature the rear gets hot air. This is because in a normal case the valve is open and air guides shut the warm air path when moderate cooling power is needed (heater core is hot which allows the air temperature being accurately controlled by flaps) but when maximum cooling capacity is required, the system closes the water valve and opens the hot air flaps to increase air flow. In a normal case the air should be cool because hot water flow to the heater core is closed. But if the valve is stuck open, the heater core remains hot and the rear of the car gets hot air because of the open hot air flaps.

 

[christopherwk]

MB squeezed every penny from you

Yes, they charge you for everything, even if they remove a wheel (£24.80 + VAT) - this wasn't do to with this though.

Anyway, £186.00 of the bill was just to bleed the brakes, and £37.20 to deactivate/activate SBC!

Also looking at the DIY link Diesel Benz just posted suggest it has nothing at all to do with the brakes!

Obviously, I don't use main dealers anymore!

 

[Timmy M]

Now that sounds odd. The official workshop instructions do not suggest removal of the brake pedal (see AR8325P1140T). Also if you look at this DIY guide, it actually is a DIY job and many owners have completed the task.
DIY: Installing a new Changeover/Heater Control Valve - MBWorld.org Forums

I cannot remember the date the part was changed but obviously the new part should hold better. The 2-zone AC has a different valve part, not sure if those fail equally, there is a modified part anyway.

The issue with the 4-zone system is that the valve gets stuck and either you do not get warm air at cold outside temperature (valve stuck closed) or at very hot ambient temperature the rear gets hot air. This is because in a normal case the valve is open and air guides shut the warm air path when moderate cooling power is needed (heater core is hot which allows the air temperature being accurately controlled by flaps) but when maximum cooling capacity is required, the system closes the water valve and opens the hot air flaps to increase air flow. In a normal case the air should be cool because hot water flow to the heater core is closed. But if the valve is stuck open, the heater core remains hot and the rear of the car gets hot air because of the open hot air flaps.

I think that with 4 zone A/C the positioning of the faulty valve may be slightly different to a 2 zone. It is positioned directly below the brake fluid reservoir and this was the reason for the guy disconnecting the brake pedel. He then "moved" the reservoir with all pipework attached, which gave him very easy access to the valve. I am just so happy that I have now got working climate control as I am like a bear with a sore head when things are not perfect with my car! as I am sure most of the people who use this forum are. Incidently I have defected from Audi after 9 years and I can honestly say that my 2004 W211 knocks spots off my "old" 2007 A6 and am looking forward to many years of pleasurable Mercedes motoring!

 

[Diesel Benz]

I think that with 4 zone A/C the positioning of the faulty valve may be slightly different to a 2 zone. It is positioned directly below the brake fluid reservoir and this was the reason for the guy disconnecting the brake pedel. He then "moved" the reservoir with all pipework attached, which gave him very easy access to the valve. I am just so happy that I have now got working climate control as I am like a bear with a sore head when things are not perfect with my car! as I am sure most of the people who use this forum are. Incidently I have defected from Audi after 9 years and I can honestly say that my 2004 W211 knocks spots off my "old" 2007 A6 and am looking forward to many years of pleasurable Mercedes motoring!

Did you notice that the DIY guide was for a 4-zone AC car! From your first post I read your car also has the 4-zone system. WIS does not make a difference either between the two options.

But perhaps the RHD car is built differently and that could explain the difference and the need to work with the SBC brakes?

 

[Soltan]

Excellent post Timmy M and good timing too, I noticed this on my car the other day, although it seemed to have fixed itself yesterday

Based on christopherwk's experience, might be good for a laugh to get a quote from the dealers Over £600 to replace a £25 part! OUCH!

 

[Timmy M]

Did you notice that the DIY guide was for a 4-zone AC car! From your first post I read your car also has the 4-zone system. WIS does not make a difference either between the two options.

But perhaps the RHD car is built differently and that could explain the difference and the need to work with the SBC brakes?

Diesel Benz, I see your point and yes maybe rhd versions may be different, also I am no expert (yet) but is the engine in the DIY guide a V6 or straight 6?? either way I am happy that my AC now works fully :bannana:

 

[Timmy M]

Excellent post Timmy M and good timing too, I noticed this on my car the other day, although it seemed to have fixed itself yesterday

Based on christopherwk's experience, might be good for a laugh to get a quote from the dealers Over £600 to replace a £25 part! OUCH!

Soltan, my issue only raised its ugly head when the outside temp was above about 25-6C if it was below that ( an evening drive maybe ) it worked ok. Hope you can find an engineer who can help.. if I can be of any more assistace plrease get in touch

 

[Diesel Benz]

Diesel Benz, I see your point and yes maybe rhd versions may be different, also I am no expert (yet) but is the engine in the DIY guide a V6 or straight 6?? either way I am happy that my AC now works fully :bannana:

Yes, the car from the DIY link was a MY 2004 E320 gasser, a V6 engine while you seem to have an I6 engine. But the parts at the firewall area are not differently positioned for different engines.

If you find a good document explaining a difference between the RHD and LHD models, let me know, I would certainly be interested because it is often difficult to find this info from WIS.

As you say, the fact that your air conditioning is working is what really matters now.

 

[Timmy M]

Yes, the car from the DIY link was a MY 2004 E320 gasser, a V6 engine while you seem to have an I6 engine. But the parts at the firewall area are not differently positioned for different engines.

If you find a good document explaining a difference between the RHD and LHD models, let me know, I would certainly be interested because it is often difficult to find this info from WIS.

As you say, the fact that your air conditioning is working is what really matters now.

DB, Its great that we all share ideas etc.. as they say many hand make lite work. I look forward to resolving further issues . keep on posting!!