HEATER BLOWING COLD - SOLVED - W219 CLS

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Teego

MB Enthusiast
Joined
Feb 2, 2018
Messages
2,130
Location
Derbyshire
Car
CLS55 AMG
A few day ago I lost all cabin heating.
Fan, flaps, aircon and coolant level all good.
So, as you do, I trawled the net. The problem was the duo valve which would not open to pass hot "water" to the heater. This is a common problem.
The valve is not too expensive but it sits under the brake fluid reservoir (on RHD cars) and is a pig to get at.

Long story short, this is what I did:
1. Warm the engine to normal temperature
2. Select Hi on the heater controls with aircon off.
3. Locate the duo valve with a torch
4. With a length of softwood tap the valve repeatedly. I didn't use a hammer or any violence as the valve is plastic.
5. I then alternated between Hi and Lo several times as quickly as I could. Still blowing cold.
6. With the setting on Hi I turned the engine off and tapped the valve again several times - firmly but not enough to damage it
7. With the engine still off to relieve any "water" pressure on the valve, and ignition on I toggled several times between Hi and Lo.
8. Not hoping for much, I restarted the engine and set the heater to Hi - hot air flowed.
9. To test that all was well, I took a 10 mile drive
10. SORTED
 
Well done, but don't expect your solution to be permanent. Your duo valve is probably going to fail completely at some point. Get it changed. A good indy can do the job in under an hour.

This was the state of the one taken out of my last E55.hcj4K00.jpg
 
This ^ +1.
 
Don't spoil my party. If it eventually fails to respond to treatment I'll change it. Meanwhile it works.
I only posted because it may help others. FFS.
 
Don't spoil my party. If it eventually fails to respond to treatment I'll change it. Meanwhile it works.
I only posted because it may help others. FFS.
I guess my well meant advice isn't wanted. Fair enough.
No party spoilt.
 
A few day ago I lost all cabin heating.
Fan, flaps, aircon and coolant level all good.
So, as you do, I trawled the net. The problem was the duo valve which would not open to pass hot "water" to the heater. This is a common problem.
The valve is not too expensive but it sits under the brake fluid reservoir (on RHD cars) and is a pig to get at.

Long story short, this is what I did:
1. Warm the engine to normal temperature
2. Select Hi on the heater controls with aircon off.
3. Locate the duo valve with a torch
4. With a length of softwood tap the valve repeatedly. I didn't use a hammer or any violence as the valve is plastic.
5. I then alternated between Hi and Lo several times as quickly as I could. Still blowing cold.
6. With the setting on Hi I turned the engine off and tapped the valve again several times - firmly but not enough to damage it
7. With the engine still off to relieve any "water" pressure on the valve, and ignition on I toggled several times between Hi and Lo.
8. Not hoping for much, I restarted the engine and set the heater to Hi - hot air flowed.
9. To test that all was well, I took a 10 mile drive
10. SORTED
Hi,does the AC still works ok since you "tapping" fix?
 
Had the same problem on my W219 - the tapping didn't last that long and bit the bullet and had the valve changed - so much better
 
Time to source a replacement duo valve before winter arrives methinks 🤔
Are you sure is duo valve? I thought i had a duo valve problem but actually is a AC leak that causes more warm air in the right vents
 
That sounds more like a heater flap problem. I can't see how a refrigerant leak could cause that. If a 'specialist' told you that, I'd seek a second opinion.
 
That sounds more like a heater flap problem. I can't see how a refrigerant leak could cause that. If a 'specialist' told you that, I'd seek a second opinion.
It's 100% a leak. Topped up the AC,then a few days later the AC light blinks and stops the ac automatically due to no pressure.
In between, nice cold air in all vents for a few days.
Climate control works as nornal,hot and cold air in all vents etc.
Just before the AC runs out (due to leak) i only have cold air on the left side of the vents for 30 min or so then the AC system shuts itself off due to no pressure(red light blinks).
But i still got normal cold(not AC) air and hot air coming from vents when select.
 
Last edited:
A few day ago I lost all cabin heating.
Fan, flaps, aircon and coolant level all good.
So, as you do, I trawled the net. The problem was the duo valve which would not open to pass hot "water" to the heater. This is a common problem.
The valve is not too expensive but it sits under the brake fluid reservoir (on RHD cars) and is a pig to get at.

Long story short, this is what I did:
1. Warm the engine to normal temperature
2. Select Hi on the heater controls with aircon off.
3. Locate the duo valve with a torch
4. With a length of softwood tap the valve repeatedly. I didn't use a hammer or any violence as the valve is plastic.
5. I then alternated between Hi and Lo several times as quickly as I could. Still blowing cold.
6. With the setting on Hi I turned the engine off and tapped the valve again several times - firmly but not enough to damage it
7. With the engine still off to relieve any "water" pressure on the valve, and ignition on I toggled several times between Hi and Lo.
8. Not hoping for much, I restarted the engine and set the heater to Hi - hot air flowed.
9. To test that all was well, I took a 10 mile drive
10. SORTED
You own a Amg don't be tight, replace it slim.
 

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