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Discussion Starter #1 (Edited)
I have a most perplexing problem on my E320. The left side(this is a right hand drive model) blows cold air with the ac on and the temp set to low, but the right side blows cool air, not cold.

My first thought was the heater valve, which I replaced. No different...
So, out with the MB Star, only to discover no fault codes. I went into actuations, and eventually came up with a problem on the right side vent motor. I pulled the dash, and removed the heater box. I discovered that the right upper vent stepper motor had jumped out of its socket because of distortion, so I modified the arm to ensure that it would not jump out again, replaced the dash and retried.

Same problem, only now the problem I had noticed earlier with slightly less air on the right vent as compared to the left was now corrected, so I had made progress, although only baby steps...

So, out with the MB Star, still no faults, and then into actuations, and still no faults, all ok...

So, I removed the dash again, removed the heater box and went hunting. I noticed that the right side upper air blend flaps were not sealing off entirely, or, more accurately, the plastic drive was reaching its stop fractionally before the stop was reached on the actual air blend flaps within the heater,so I modified the stop to allow the air blend doors to reach their stop first...then I replaced everything,.... re initialized all the stepper motors,.... and no different...

Now I have a new fault, the air quality sensor comes up as faulty, but it still blows warm air out the right vent.

Now I also note the rear vents blow hot air, piping hot air... This led me to look at the heater valve once more, as with all temperature controls set to low, including the rear, the heater valve should be closed., and it obviously is not.

I went into the heater valve on mb star, and did the heater valve test. I closed the valve with the MB Star tester, and yet hot air continued to pour out after an allowable cooling time for the heater core.. So, the new valve appears faulty, however, the heater aux water pump continues to run, and it can only get its command from the control unit, in conjunction with the heater valve its self....

Can anyone help me with this problem???? Any thoughts and advice would be most helpful!!!
 

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Have you ever checked the freon? Mine used to blow cooler air on the right side, and after adding some freon the problem was gone. Good luck.
 

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Discussion Starter #4
To remove the heater box, the refrigerant is removed, and obviously replaced with the correct quantity when refilled, so thats not the problem ....
 

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To remove the heater box, the refrigerant is removed, and obviously replaced with the correct quantity when refilled, so thats not the problem ....
I'll start by qualifying this: I have more experience with BMW that Mercedes. Just got our first E class.

To remove a heater box (sometimes called heater core) you usually loose coolant, not refrigerant. Coolant is the blue liquid that flows through the radiator. Refrigerant is the gas (used to be freon, now r 'something', r12) in the AC system. I'm not positive on the W211, but you should not have to drain that to deal with the heater box, typically that is coolant you deal with.

Again with BMW, but lack of cold air on passenger side compared to driver is usually due to low AC refrigerant (r12) pressure. Have you tested the AC system pressure?
 

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Discussion Starter #8
Thank you all for your responses, all help, and advice is welcomed...

To those who are unsure, let me tell you what is involved in removing the heater box...

Remove carpets, both front...
Remove centre console, complete...
Remove instrument cluster
remove heater controls
remove radio and all its hardware
remove upper dash, complete
remove lower dash, complete
remove wiper mechanism, complete
remove refrigerant, and then remove pipes at the expansion valve
remove fuse box, remove heater piping at the heater valve
remove dash cross brace, a large aluminum bracket running the entire length of the dash...
remove handbrake assembly
remover heater box.....

So, refrigerant is removed, and when re assembled, it is replaced.... and the coolant pipes to the heater core is also removed...
 

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I went into the heater valve on mb star, and did the heater valve test. I closed the valve with the MB Star tester, and yet hot air continued to pour out after an allowable cooling time for the heater core.. So, the new valve appears faulty, however, the heater aux water pump continues to run, and it can only get its command from the control unit, in conjunction with the heater valve its self....
The heater valve should not create different temperature on one side. Did you actually check that the valve works when controlled by DAS? Every now and then the front SAM gets broken, most likely caused by a failed heater valve. If you use DAS actuations to close the valve, you really should not have hot air coming from the HAVC system.

Note that the heater valve (Heat exchanger shutoff motor) does only closes when extreme cooling is needed. The idea is to open flaps that otherwise would bring hot air but do not after the valve is closed and then more air can flow through the AC system.
 

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Discussion Starter #10 (Edited)
Aahhh now we are talking...!
I did close off the heater valve through DAS, and no, it did not close... However, the curious thing is the aux water pump/heater water pump , which, to my knowledge only operates when the heater valve is open, is running...

Now, I did not know that the heater valve is controlled by the forward sam unit... is this a definite??

I am still trying to figure out why the valve does not close...., again, you mention the forward SAM unit... Have you had and dealt with this issue before??

I am aware that the heater will have hot water flowing through it anytime the ac ECU decides that it has to heat the air to bring the cabin to the required temperature... However, in this case, all temp controls were set to 'Lo' and ambient temp was about 24 deg C, so the heater valve should not have been open. It was after experiencing the warm air at the rear vents that I noticed the valve was not shut of, and then went through DAS and closed the valve. The blower was then set to high, but the air never cooled down at all...
 
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