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Registered
92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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Discussion Starter #1
Hi,
My electrician has just given up on my 1992 500SL AC issue.
This is the case: the AC starts to blow cool air and pretty soon it stops,after a few minutes it blows again for a minute or so and stops again...
Any advice guys?
Best Regards
Chris
 

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2000 SL500
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381 Posts
Hi,
My electrician has just given up on my 1992 500SL AC issue.
This is the case: the AC starts to blow cool air and pretty soon it stops,after a few minutes it blows again for a minute or so and stops again...
Any advice guys?
Best Regards
Chris
When you say the cool air stops do you mean the air flow stops or the air flow continues and the cool air turns warm? Is the blower motor stopping? If it's not the air flow stopping and the air is turning warm have you checked to see if the compressor clutch is disengaging at this time?
 

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Registered
92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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83 Posts
Discussion Starter #4
When you say the cool air stops do you mean the air flow stops or the air flow continues and the cool air turns warm? Is the blower motor stopping? If it's not the air flow stopping and the air is turning warm have you checked to see if the compressor clutch is disengaging at this time?
The latest: the air keeps flowing except it stops being cool and then after a few minutes it comes back to the cool flow. It also happens when I turn the AC to "low" when it should blow cold continously. I'll talk to the mechanic about the clutch. In case Im
still in trouble I will ask for your help again.
Thanks!
 

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Registered
92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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83 Posts
Discussion Starter #5
When you say the cool air stops do you mean the air flow stops or the air flow continues and the cool air turns warm? Is the blower motor stopping? If it's not the air flow stopping and the air is turning warm have you checked to see if the compressor clutch is disengaging at this time?
My mechanic says something about the" CFC sensor power supply error" and told me to look for a diagram- could you please help with that?
 

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Outstanding Contributor
2003 SL500, 2003 SL55, and four R129s
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4,376 Posts
This is the case: the AC starts to blow cool air and pretty soon it stops,after a few minutes it blows again for a minute or so and stops again...
This is fairly easy to identify the source of the problem.

Put your climate control unit in diagnostic mode as explained here. Then monitor the temperature of the evaporator. The compressor clutch should engage/disengage repeatedly to maintain a temperature in a range of c. 32-38 degrees F. If it is doing this at a time when you are not getting cold air, then your problem is that the monovalve which regulates the flow of coolant to the heater core is not functioning properly. If the temperature of the evaporator goes above 40, then your problem is with the A/C.

Finally, you can download a complete set of wiring diagrams and the Starfinder parts locator application here.
 

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1999 ML320, 1998 SL500
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860 Posts
The A/C level is fine.
Thanks!
Good. I thought you might have checked that early on, I recently had a wild adventure with my 1998 SL500 when EC activated and prevented the compressor from running but I needed the compressor to run to allow a refrigerant to fill. I was sort of a Catch 22 situation, My '98 has a different control setup from your car but there were several helpful suggestions which helped resolve the situation. That saga was posted when I had to use a temporary ID of CalCiCi.
 

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92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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83 Posts
Discussion Starter #12
Still no solution to the issue...My electrician says all the tests show no error and the compressor would work fine except there is a problem with the CFC sensor power supply.Still looking for a reason.
Looks more and more complicated
 

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2003 SL500, 2003 SL55, and four R129s
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I have the notion you used diagnostics to read fault codes, but that wasn't what I had in mind. You are interested in seeing what the evaporator temperature sensor is reporting. That is Test mode A, step 06. You ought to have a look at the heater temperature sensor as well (step 08).
 

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92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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83 Posts
Discussion Starter #14
I have the notion you used diagnostics to read fault codes, but that wasn't what I had in mind. You are interested in seeing what the evaporator temperature sensor is reporting. That is Test mode A, step 06. You ought to have a look at the heater temperature sensor as well (step 08).
Bobterry,
My electrician is reporting that the step 6 shows "lo"
 

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2003 SL500, 2003 SL55, and four R129s
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...
My electrician is reporting that the step 6 shows "lo"
That value is not defined by the diagnostic manual.

In lieu of step 06 you can troubleshoot off of step 08. The heater exchanger temperature should not be very much more than ambient temperature if the monovalve is working properly. If it isn't, then likely the heater temperature will rise and fall in correlation with the temperature of the air at the vents.

Incidentally, I have no idea what a "CFC" sensor is...
 

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92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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Discussion Starter #16
That value is not defined by the diagnostic manual.

In lieu of step 06 you can troubleshoot off of step 08. The heater exchanger temperature should not be very much more than ambient temperature if the monovalve is working properly. If it isn't, then likely the heater temperature will rise and fall in correlation with the temperature of the air at the vents.

Incidentally, I have no idea what a "CFC" sensor is...
CFC shows as a translation for a "freon sensor".
The additional problem is I'm not much of a mechanic ( I'm a surgeon,for humans not vehicles ) and my car electrician does not speak English so Im just trying my best to cover both sides of this story.
Bob, I will try to explain to the electrician what your point has been so far.
I really appreciate you spend your time trying to help a complete stranger. This Benz Community is just awesome...
 

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2003 SL500, 2003 SL55, and four R129s
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There is a freon sensor, and it is an electrically passive device (i.e., it has no power supply). Since your man speaks no English and this is a very simple task, maybe you should just read the values for yourself?
 

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92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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83 Posts
Discussion Starter #18
There is a freon sensor, and it is an electrically passive device (i.e., it has no power supply). Since your man speaks no English and this is a very simple task, maybe you should just read the values for yourself?
I guess I will have to.
Thanks!
 

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92' 500SL, 93' S500 C140, 91' W126 260SE,91' Daimler Double Six
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83 Posts
Discussion Starter #19
There is a freon sensor, and it is an electrically passive device (i.e., it has no power supply). Since your man speaks no English and this is a very simple task, maybe you should just read the values for yourself?
Hey guys,
Bobterry,
The problem solved: the evaporator sensor was polluted by some grayish substance, we cleaned it and the AC is working again
Thanks to all of you!
 

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2003 SL500, 2003 SL55, and four R129s
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4,376 Posts
The compressor control is based mostly upon that sensor, so if it is reporting an inaccurate temperature the compressor will run too much or too little.
 
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