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Hello,

Thanks in advance for any assistance. I've been experiencing an intermittant heat issue with my 2005 S600. I've searched the forums for similar problems, and have tried some remedies, but have had no success at all in correcting the situation:

Symptoms:
A/C cold seems works fine. When set to HI, the heat to the front passenger vents blows **HOT** when stoped at idle or sub-35mph speeds. At higher speeds (45+), the heater blows cold like the A/C is on. I've noticed that if I turn the EC "light on" (turn off the A/C compressor) the super cold A/C effect seems to go away, but overall result is the same (cold air to front at higher speeds). Also, if I dial the center vent "mix" dial where it illuminates "auto" it blows colder, but if I dial it to the blue, it heats up (but only until higher speeds reached). The REAR heat controls seem to funtion fine at all speeds. Temperature on the gague reads between 80c and 95c which seem "normal" to me.

What I've attempted so far: Complete coolant flush, burping the system for any air (didnt' seem to be any), replaced the N22 ACC pushbutton control module (was getting the N1000 error, no errors now) AND the entire dual valve/heater control unit assembly by the front firewall (no errors pulled, but based on what I found on the forum, it seemed worth a shot). The L/R front temp sensors appear to be working normally as is the sun sensor. There are no coolant leaks or smells. I've run a flap test (option 11 in that one menu) and all seems to be working properly.

So now I am thinking the thermostat, but it confuses me that the rear controls seem to be functioning and operating temps seem to be within normal ranges. Which leads me to think something along the lines of a mix flap (maybe #4 or #5 of that W220 A/C pdf) or front heater core issue? Maybe a sensor that I'm missing?

Any thoughts or ideas on how to further diagnose or correct? I'm getting really frustrated (and my wife is starting to give me grief since she refuses to drive or ride in it with no heat) and am getting tired of throwing money at it with no result. Obviously with winter around the corner, it's becoming more of a priority to get it fixed.

THANKS!!!
__________________
2005 S600
2004 E500 4-Matic
2002 C32 AMG
2001 Trans Am WS-6

 

Well since I see a lot of views but not a lot of help, I figure I'll add more details now that I have observed the problem more.

After warming up, at idle, temp gague reads about 90', at speed on the highway it sits rock solid just above the 80' line.

All lines running to/from the dual valve assembly (which was just replaced) are very hot to the touch. The motor inside is definitely whirring (sound and feel).
If the car is shut down, the REST function does blow out hot air just fine from the front vents.

Heat to the independant rear seat controls seem to work fine at all speeds.
Heat to the front is hot at idle, but cools off as speed increases. It is definitely speed, not RPM, sensetive from what I can tell (redlined it for about a mile on the highway at constant speed in 2nd gear to see if that did anything).

There are no error codes on the A/C panel in diagnostic mode "ERRORS _ _ _ _"

After returning home from a 40 mile highway commute, I stopped in my garage with the car running, EC button on (A/C compressor OFF), and pulled the following figures from holding the REST button. Perhaps this can assist in helping me narrow down what might be wrong?

00 - 27.5
01 - 30.5
02 - 8
03 - 48
04 - 62
05 - 14.7
06 - 94
07 - 6.0 BAR
08 - 25.1
09 - 2.1k
10 - 2.9V
11thru15 - 0%
16 -63
17 - 960
18 - 9.5
(skips 19??)
20 - 0
21 - 587/min
22 - 0 km/h
23 - 99%
24 - 14V
(skips 25 & 26)
27 - 100%
28 - 0%
29 - 100%
30 - 31c
31 - 34c
32 - 31c
33 - 2.9V
34 - 23
35 - 24
36 - 128%
37 - AUF
(Skips 38 & 39)
40 thru 47 - ZU
48 - FrischL
49 - AUS
50 - 27
51 - 4198
52 - 20
53 - 85
54 - 38
55 - 10
56 - 30
57 - 05
58 - 1B
59 - 01
60 - 32
61 - 16
(skips 62-69)
70 - INAKTIV
71 - AKTIV
72 - INACTIV
73 - ACTIV
74 - GENERELL
75 - INAKTIV
76 - ZEITBEGR
77- GEN.NEG
(skips 78-79)
80 - AUTOMAT
(skips 81 & 82)
83 - MOGLICH
84 - o.SONNE
85 - AUTOMAT
86 - GEGCHL
87 - ESL
(skips 88-95)
96 - ONM
97 - 0%
98 - 0mA
99 - 30.9c

 

Man, I hate to see you put all this effort in explaining and not get replies. I can't help really, but what about asking a dealer or a good shop about this issue?

 

Going to take one more stab at requesting assistance from the forum and will probably resign myself to taking it to the dealership given the overall lack of response. Can't tell if this is something that is breaking new ground that no one is familiar with, or if no one has a clue, or if I've done something that would warrant being ignored. I made sure to do my due diligence before posting my issue by performing multiple searches as well as doing preliminary work (replacing ACC module and dual valve) before asking for help, so I don't think it's the latter...

Just took it to my indy mechanic, he specifically reversed flushed the heater core and said there was no blockage at all. He believes that it is perhaps a blend door issue. The ACC unit is not throwing any codes for a bad stepper motor (no errors at all in fact). I am, however, noticing that the sensor value for my left heater sensor (#3) is consistantly lower than my right heater sensor (#4).

Any ideas on how to diagnose a blend door issue; especially given that there are "left and right" doors? The difficuty is that it only acts up at highway speeds, so I'll need to do it while driving, or perhaps while someone else is driving for me.
Thanks again.