Rear cooling/heating help (W219 - heater control valve?)

[moodi]

Looking for some help. My new-to-me W219 CLS 55 has an issue where the rear is hot no matter what the control dial is. The front heating/cooling works fine.

I have read that it could be the heater control valve, as this topic:

[SOLVED] - Rear Aircon Hot Hot Hot!

However, the last reply leaves me less than confident.

What is the best way to diagnose / fix this?

 

[whitenemesis]

Bet way? Get the codes read using STAR

 

[moodi]

I've also heard it could be this. Would STAR tell me for sure?

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[clk320x]

Wouldn’t this be a duovalve issue?

 

[moodi]

Wouldn’t this be a duovalve issue?

Is that the heater control valve as pictured here? I heard it can be caused by that or the chip I linked.

Genuine Mercedes-Benz -CLS-Class 219 Heater Duo Valve **NEW** | eBay

 

[clk320x]

Is that the heater control valve as pictured here? I heard it can be caused by that or the chip I linked.

Genuine Mercedes-Benz -CLS-Class 219 Heater Duo Valve **NEW** | eBay

Yeah I had to have it changed on my W211. Very very common.

Pretty straight forward but access is a bit tricky.

 

[moodi]

I think access is even more tricky on the W219, the wipers/motor/assembly need to come out from what I have seen?

The part is cheap enough, but just wondering if there is a definitive diagnosis before I chuck some cash at it. STAR could be an option if someone can confirm it will show one way or the other.

 

[clk320x]

STAR could be an option

Mine didn’t have any errors on star for the duovalve

But if you are having hot air in the back and cold in the front it’s 99% going to be the duovalve

 

[moodi]

Mine didn’t have any errors on star for the duovalve

But if you are having hot air in the back and cold in the front it’s 99% going to be the duovalve

That is exactly what the symptoms are. Ok, a £30 part and 2 hours of DIY with some buddies, doesn't seem too bad for troubleshooting at minimum and hopefully a total fix!

 

[clk320x]

That is exactly what the symptoms are. Ok, a £30 part and 2 hours of DIY with some buddies, doesn't seem too bad for troubleshooting at minimum and hopefully a total fix!

Good luck pal! Also I have replied to your pm

 

[AMGeed]

My indy changed my heater control valve. Same symptoms, hot and cold at the front, hot only at the rear.
He removed the accelerator pedal and moved the SBC pump a bit to gain more access and did the job in around 30 mins. (Prior experience counts a lot I'd say)
This is the state of mine when it was opened up.

 

[moodi]

Accelerator pedal and SBC pump? Guessing yours was not a W219? (think they are in a different position)

Yikes! I'll cut mine open if this cures it and see how bad it is compared.

 

[clk320x]

Accelerator pedal and SBC pump? Guessing yours was not a W219? (think they are in a different position)

Yikes! I'll cut mine open if this cures it and see how bad it is compared.

The 211 and 219 are basically the same underneath.

I’m not sure how removing the accelerator pedal will help Rog as surely the firewall is in the way?

 

[Major774]

It will most likely be the duo valve, I have personally changed mine myself as the rear vents were blowing hot air.

In the meantime, you can trick the system to work when you get the hot rear vent issue. If I remember correctly, turn the front two temp. settings to high and run it until you feel cold air blowing out the rear vents. Then you can lower the front temps and the rear vents should keep cool.

 

[AMGeed]

Accelerator pedal and SBC pump? Guessing yours was not a W219? (think they are in a different position)

Yikes! I'll cut mine open if this cures it and see how bad it is compared.

Yep, I thought it strange but it made access so much quicker.
The 219 shouldn't be any different to my 211 for this job.

The 211 and 219 are basically the same underneath.

I’m not sure how removing the accelerator pedal will help Rog as surely the firewall is in the way?

Thats the way an experienced indy did it Abs. I wasn't going to argue.
What made it worse for the poor guy, the OEM valve supplied was faulty and he had to do it twice.