w124 e320 climate control issues
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Joined: Nov 2025
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1994 E320
w124 e320 climate control issues
good afternoon everyone ! i have been putting this off for a while but its to the point where im loosing my mind .
here is my issue and i hope someone can help .
my e320 has been having a following climate control issue .
when its turned on , it will work fine, brings the temperature to what its set to but fan keeps going and wont change speed ( wont slow down or shut off ) but!! its not the case every time . randomly it starts working fine , and then its back to its old self .
i dug in to it , so far i tested blower motor which works fine, ait sampler motor was not turning off due to bad resistor ( replaced it so it runs now) , i had a luxury of being able to borrow numerous climate control panels from a shop and none of them made a difference .
after i put a new sampler motor in today , it worked great for about 45 minutes before i shut the ignition off, then it went back to its old seld . keeps trying to mix hot air with cold and keeps blowing air at high speed continuesly .
has anyone had this issue before ? any ideas what to look in to ? i tried to look at all available information online but i got nothing . i cant be the only one with this problem . any help would be appriciated !!
thanks in advance !!
here is my issue and i hope someone can help .
my e320 has been having a following climate control issue .
when its turned on , it will work fine, brings the temperature to what its set to but fan keeps going and wont change speed ( wont slow down or shut off ) but!! its not the case every time . randomly it starts working fine , and then its back to its old self .
i dug in to it , so far i tested blower motor which works fine, ait sampler motor was not turning off due to bad resistor ( replaced it so it runs now) , i had a luxury of being able to borrow numerous climate control panels from a shop and none of them made a difference .
after i put a new sampler motor in today , it worked great for about 45 minutes before i shut the ignition off, then it went back to its old seld . keeps trying to mix hot air with cold and keeps blowing air at high speed continuesly .
has anyone had this issue before ? any ideas what to look in to ? i tried to look at all available information online but i got nothing . i cant be the only one with this problem . any help would be appriciated !!
thanks in advance !!
Out Of Control!!
Joined: Apr 2019
Posts: 11,957
Likes: 6,796
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
no live data
good afternoon everyone ! i have been putting this off for a while but its to the point where im loosing my mind .
here is my issue and i hope someone can help .
my e320 has been having a following climate control issue .
when its turned on , it will work fine, brings the temperature to what its set to but fan keeps going and wont change speed ( wont slow down or shut off ) but!! its not the case every time . randomly it starts working fine , and then its back to its old self .
i dug in to it , so far i tested blower motor which works fine, ait sampler motor was not turning off due to bad resistor ( replaced it so it runs now) , i had a luxury of being able to borrow numerous climate control panels from a shop and none of them made a difference .
after i put a new sampler motor in today , it worked great for about 45 minutes before i shut the ignition off, then it went back to its old seld . keeps trying to mix hot air with cold and keeps blowing air at high speed continuesly .
has anyone had this issue before ? any ideas what to look in to ? i tried to look at all available information online but i got nothing . i cant be the only one with this problem . any help would be appriciated !!
thanks in advance !!
here is my issue and i hope someone can help .
my e320 has been having a following climate control issue .
when its turned on , it will work fine, brings the temperature to what its set to but fan keeps going and wont change speed ( wont slow down or shut off ) but!! its not the case every time . randomly it starts working fine , and then its back to its old self .
i dug in to it , so far i tested blower motor which works fine, ait sampler motor was not turning off due to bad resistor ( replaced it so it runs now) , i had a luxury of being able to borrow numerous climate control panels from a shop and none of them made a difference .
after i put a new sampler motor in today , it worked great for about 45 minutes before i shut the ignition off, then it went back to its old seld . keeps trying to mix hot air with cold and keeps blowing air at high speed continuesly .
has anyone had this issue before ? any ideas what to look in to ? i tried to look at all available information online but i got nothing . i cant be the only one with this problem . any help would be appriciated !!
thanks in advance !!
The main issue is the lack of OBD live data to troubleshoot 1994 chassis.
Based on your work and inputs, remaining culprits may be...
- cabin filter air flow
- blending door flap module
- rotary sensor fan stuck
- low or high refrigerant pressure
- marginal local GND or +12V circuit
I absolutely hate replacing parts blindly because of low success rate.
My top guess would be a bad sensor because it is nearly working well.
Try to force select top side output to see if footwell gas the standard broken sensor...
Happy Holidays to you...
Last edited by CaliBenzDriver; Nov 27, 2025 at 11:20 PM.
Thread Starter
Newbie
Joined: Nov 2025
Posts: 3
Likes: 1
1994 E320
You have done a fair amount of parts swapping. This can still be a number of things.
The main issue is the lack of OBD live data to troubleshoot 1994 chassis.
Based on your work and inputs, remaining culprits may be...
I absolutely hate replacing parts blindly because of low success rate.
My top guess would be a bad sensor because it is nearly working well.
Try to force select top side output to see if footwell gas the standard broken sensor...
Happy Holidays to you...
The main issue is the lack of OBD live data to troubleshoot 1994 chassis.
Based on your work and inputs, remaining culprits may be...
- cabin filter air flow
- blending door flap module
- rotary sensor fan stuck
- low or high refrigerant pressure
- marginal local GND or +12V circuit
I absolutely hate replacing parts blindly because of low success rate.
My top guess would be a bad sensor because it is nearly working well.
Try to force select top side output to see if footwell gas the standard broken sensor...
Happy Holidays to you...
).ill post the outcome after resistor is installed .
Out Of Control!!
Joined: Apr 2019
Posts: 11,957
Likes: 6,796
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
thanks for the repy ! so dug in to it deeper after i posted this , ac compressor builds pressure and runs as it should, blender door module was visually operating perfectly without any delays . slightly started leaning towards bad blower motor resistor . i ordered a manual fot it as well. someone also mentioned bad blending ( duo ) valve but that should not be the case since it does bring hot air in . parts budget is about $150 , and if this does not solve it then im going to start with making a standalone harness for heat/ac unit . this thing is just a headache from what i was able to understand ).
ill post the outcome after resistor is installed .
).ill post the outcome after resistor is installed .
Do you have a hot water valve to the heater core? They routinely to fail stuck halfway.
The resistor ladder increasingly drops voltage to the motor. Make sure the motor plug is not toasted and again that you have good GND/PWR using a DVMeter. This is 10+Amps circuit... high power.
Climate control is mandatory function for winter driving else the windshield fogs up on the inside.
Manual operation is better than nothing.
Thread Starter
Newbie
Joined: Nov 2025
Posts: 3
Likes: 1
1994 E320
fixed. it was due to bad blower motor resistor that never stopped working, and worked fine when it wanted to ... unit is quiet and quick to bring temperature to what its set to . i do have to replace foam padding around blender doors now , it has turned in to dust and you can hear hissing sometimes .
thanks for your help !
thanks for your help !
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