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99 ML320, 02 ML55, 95 740i, 85 745i
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35 Posts
Discussion Starter #1
even when AC is on. The AC could be cold and then all of the sudden the air would turn hot and stays hot.

After stopping the car with the engine off for a while the AC works again after restart but hot air would return with no apparent tell tale sign.

It happens randomly and it is very hard to decide when it is going to blow hot.

Fuse has been changed to 40A and all flaps work properly. :confused:

Help!
 

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2000 ml430, 99 infiniti i30 limited edition
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980 Posts
read the manual on how to operate the climate control system. Its tricky. I think they should have made it easier to use like in a honda or nissan.
 

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2002 honda civic (sold), 2009 Mercedes ML350
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ecartoys said:
even when AC is on. The AC could be cold and then all of the sudden the air would turn hot and stays hot.

After stopping the car with the engine off for a while the AC works again after restart but hot air would return with no apparent tell tale sign.

It happens randomly and it is very hard to decide when it is going to blow hot.

Fuse has been changed to 40A and all flaps work properly. :confused:

Help!
why did you change a fuse to a higher rating fuse? that is something you do not do. circuits have fuse ratings for a reason.

anyway, sounds like it could be a evap temp sensor. alot of times the car starts off cold then gets warm.
 

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2002 ML 500, 1994 Ford Explorer donated to Doctors without Borders
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2,126 Posts
The plastic air mixing flap is prone to breakage. I had mine replaced at 59K. The symptoms were either very hot air or very cold air and there was nothing I could do to change or control it.
 

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99 ML320, 02 ML55, 95 740i, 85 745i
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35 Posts
Discussion Starter #5
LOL busoptr. Have owned the ML320 since new and we live in Palm Springs so it is safe to say that we know how to operate the controls.

Streetglower,

I replaced the fuse based on recommendation from other threads on this board. The guy says the pre-2000 models all have 30A fuse when it should have been 40A. Anyway I confirmed it with the dealer before it was changed.

Bogie,

Any idea how one can inspect the plastic air mixing flap?


Thanks all.
 

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ML320 CDI 2006 SAAB 9-3 Convertible 2004
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68 Posts
Had a similar problem with my 2000 ML, it turns out the radiator fan is broken and the gas is low, so when the aircon is on and the vehicle is stopped, the fans on the condenser are not able to move all the heat. Gets cool again when the car starts moving again.
 

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99 ML320, 02 ML55, 95 740i, 85 745i
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35 Posts
Discussion Starter #7
ml_saab,

The aux fan is working properly and the freon/R134 is full. It is confirmed at 2 difference shops. The dealer had already replaced the condenser under warranty and now they are saying it is the AC control panel. However this time the car is out of warranty already and I am not ready to pay just to find out if they are right.

The Hot air stays on even when the AC is not on. So it is not just an AC issue.

Thanks.
 

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ML320 CDI 2006 SAAB 9-3 Convertible 2004
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This does sound like a control issue. If your AC is tested good (compressor is working, gassed up etc) and hot air is blowing means the heater core valve is open. There could be a problem with the valve itself, but just as likely the controller.
 

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2002 ML 500, 1994 Ford Explorer donated to Doctors without Borders
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ecartoys said:
Any idea how one can inspect the plastic air mixing flap?
Unfortunately no. They worked on the car over a 6 day period and I wasn't able to see the dash removed. I wonder if someone has a schematic of the a/c system.

If it's the control system, can you buy it and replace it yourself? It should be plug and play.
 

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ML320 CDI 2006 SAAB 9-3 Convertible 2004
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I found a description of the climate control system at Mercedes-Benz M-Class Climate. It says that there is no heater control valve, the heater core is hot all the time, and the air mix damper door is regulated to allow air through the heater core, controlled by the air conditioning/heating control module (N19).

There is a lot of valuable information on that page, from my reading it sounds like your damper door is not being controlled properly, and this points to the control module.
 

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99 ML320, 02 ML55, 95 740i, 85 745i
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35 Posts
Discussion Starter #11
Thanks all. Looks like I am down to mixing flap or N19 module.

Anyone has instruction, manual or info I can get to on how to replace or inspect those two parts listed above?
 

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I have the same problem. Reference link below.
http://www.benzworld.org/forums/w163-m-class/1298822-hot-air-blowing-even-when-i-dont-turn-2.html

N19 is the A/C pushbottom control module and it looks to be the source of the problem, but I’m certainly not sure.
Intermittent problem with blend air door sometimes not closing completely. Result is heat coming thru vents when temperature control turned to cold. Can not pull codes for this problem on this model, a 1999 ML 320, not automatic climate control.

Problem seems to occur when vehicle is cold and knob is turned to allow heat to enter cabin. When I want to shut it off blend air motor will not fully shut door. I’ve installed new blend air motor; did not cure problem. Blend air door not clicking or popping, in other words I don’t think it’s sticking. I can observe linkage and watch it go thru full range of motion or partial range depending on whether it’s working right or not. I can put my finger on linkage and feel it go thru it’s range, either full or incomplete and it seems quiet, fast and smooth.

I’m thinking maybe the blend air motor is not getting proper signals. I found an amplifier, MB part# 163-820-01-97 ( number is vin specific) which has Denso # TN277300-0471. I examined circuit board and could not find any obviously problems like burn marks or cracks.

Can not get any information from dealer regarding any pattern failure, they are very tight lipped.
 

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99 ML320, 02 ML55, 95 740i, 85 745i
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35 Posts
Discussion Starter #13
ron in sc said:
I have the same problem. Reference link below.
http://www.benzworld.org/forums/w163-m-class/1298822-hot-air-blowing-even-when-i-dont-turn-2.html

N19 is the A/C pushbottom control module and it looks to be the source of the problem, but I’m certainly not sure.
Intermittent problem with blend air door sometimes not closing completely. Result is heat coming thru vents when temperature control turned to cold. Can not pull codes for this problem on this model, a 1999 ML 320, not automatic climate control.

Problem seems to occur when vehicle is cold and knob is turned to allow heat to enter cabin. When I want to shut it off blend air motor will not fully shut door. I’ve installed new blend air motor; did not cure problem. Blend air door not clicking or popping, in other words I don’t think it’s sticking. I can observe linkage and watch it go thru full range of motion or partial range depending on whether it’s working right or not. I can put my finger on linkage and feel it go thru it’s range, either full or incomplete and it seems quiet, fast and smooth.

I’m thinking maybe the blend air motor is not getting proper signals. I found an amplifier, MB part# 163-820-01-97 ( number is vin specific) which has Denso # TN277300-0471. I examined circuit board and could not find any obviously problems like burn marks or cracks.

Can not get any information from dealer regarding any pattern failure, they are very tight lipped.
Hi Ron,

Any progress on yours? I have checked the blend air flap and it is working properly - I can see it moves with no popping. The MB part# you listed in not coming up on my parts database so it might be a MB dealer only parts. You mentioned that it is a VIN# specific part so I am guessing you got the part# from a MB dealer. Is the part what they listed as the N19?

Thanks.

David
 

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1999 ml320
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I found a description of the climate control system at Mercedes-Benz M-Class Climate. It says that there is no heater control valve, the heater core is hot all the time, and the air mix damper door is regulated to allow air through the heater core, controlled by the air conditioning/heating control module (N19).

There is a lot of valuable information on that page, from my reading it sounds like your damper door is not being controlled properly, and this points to the control module.
link is dead any links to how to replace n19 module on a 99 ml320? thnx bb
 

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Dallas, Texas
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link is dead any links to how to replace n19 module on a 99 ml320? thnx bb
That thread is over 12 years old.

From right side look between console and the dash. Rectangular box with 12 pin connector. Pull connector off and plug new one in. N19 is held in place with single screw accesible after removing radio and wood trim.

2019-12-15_121820.png
 

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ok got it and appreciate but what is the other n19 for and do? link is in thread just looked at it this am thnx bb
There is only one N19. It compares in car temp and desired temp. Drives blending flap hot or cold to regulate temperature.
 

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1999 ml320
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ok i understand what u r saying, and i plan on buying it, but what im wanting to kno is u say there is only 1 "n19" ?.... then what is this ?
Allen Bradley N19 Overload Relay Heater Element
pix also included
 

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Registered
Dallas, Texas
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6,985 Posts
ok i understand what u r saying, and i plan on buying it, but what im wanting to kno is u say there is only 1 "n19" ?.... then what is this ?
Allen Bradley N19 Overload Relay Heater Element
pix also included
I have no clue what it is. Picture is smaller then my mouse pointer.
 
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