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  #1  
Old 07-03-2003, 02:29 PM
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Join Date: Sep 2002
Posts: 134
124 Acc

This is my first post, I would like to thank all people in this site for their help and advice, I learned alot of information
My car is 124 300DT 1987, running good with @175K miles...

I have a problem with the ACC [AC], I started trouble shooting, there are 4 main concerns:
[since this is a repeated problem I appreciate more explanations, I did search(s) in this issue, there is alot of info., but not organised in a good sequence for diagnosing the problems...I appreciate more detailed explanations so that this post could be a source for many users]

1. getting the compresser to engage:

1.1. It starts and engages for "some time" and disengage, usually less than 1 minute. The time depends on whether the AC [clutch] was working before; if I jumped the terminals [klima input 5, and 7], the clutch engages. Letting the compressor works for sometime, then install the klima, system works for longer time, 5 minutes or so... Also, up and down RPM would cut the compressor [with klima]. [I do not know why this behavior]

1.2. I checked the output signal of the compressor RPM sensor, at the klima inputs...it is less than 0.1v at idle, and can increase to 0.2 or 0.3 v...which does not match the minimum required [0.3v at idle]. SO I need advice on how to replace the compressor sensor [ do I have to discharge the system, is the sensor in touch with refrigerant, does the pressure affecting the sensor output - may explain the previous behavior, could be the compressor bad, and replacing sensor will not help, is there a way to clean/verify the sensor is working....please advice]

1.3. The signal of engine speed (RPM), it comes to the Klima at about 10 - 11 V, in the diagnostics, it suppose to be (more than 4 v) I am not sure if this is acceptable!!!???. Also, this signal stays within this limit even with higher RPM, I think they have this as steady and the klima compares the compressor speed to this signal..the klima cuts the compressor if its speed is out of ceratin range for few seconds or so (usually between 5 to 30%, as I read in other place not mercedes)

2. Another technical issue, the signal comming from the ACC bush-buttons unit, that tells the Klima [little brain activates the compressor if everything is OK!!] to activate the compressor, this signal is available at the pressure switch [red]..It suppose to be negative (ground)...when I tested it, it was (+), possitive battery voltage...I accepted that there could be different systems with different signals...BUT the same signal comes to the Klima at terminal 10, and the diagnostic says that this is a negative...I tested there and it was a negative ...I am totally confused, how a possitive signal can be converted to negative!!!??? please help me on that...

3. System pressure seems to be OK, no leak, always engages [no need to jump the pressure switch terminals]. however, it happened that the clutch was slipping when hot, could this be because of high pressure building up [the aux. fan is not working]. Or the clutch needs cleaning [oil inside], or bad clutch...
please advice me on how to take the clutch out and clean it, without discharging the system.

Again, thank you for your help and the time you spend in reading and advicing...
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  #2  
Old 07-03-2003, 09:15 PM
J.HIDALGO's Avatar
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Join Date: Jul 1999
Location: Jax, FL
Posts: 1,785
Why are you aux. fans not working?

That alone, will kill your compressor in NO time. More info...
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'86 300E
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  #3  
Old 07-05-2003, 10:26 PM
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Thanks J.HIDALGO,
The AC did not work since I owned the car...so there was no need to fix the aux. fan (slow speed)...the fan higher speed works fine if the car is overheat...I started by fixing the AC as it is the hardest problem??? the fan might need a new relay or resistor...
I need help on how to replace the rpm sensor on the compressor clutch, without discharging the system...I am not sure if it is in contact with pressurized refrigirant inside the compressor,
thanks
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  #4  
Old 07-05-2003, 10:53 PM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Were your readings in AC voltage? I would not critique the speed sensor with voltage alone. It should be a sine wave with .3v peak to peak. A scope is a much better tool. The system does need to be discharged and most speed sensor problems are from rebuilt compressors that have the distance from the sensor to shaft defective. Speed sensor problems are common but they are almost never the sensor itself. It is more likely a belt or slipping clutch problem

The symptoms you describe characterize a loose or worn belt. Any belt flop will set off the speed sensor trigger.

It is the diesels that have the power switched Klimas, but I don't think yours is one of them. The problem is simple though since yyou do have moments of compressor action. During a moment of proper funtion look at the signalpassing through the low pressure switch. It will either be a 12v signal from the Klima that is taken to .15-.2v by the pushbutton controller. Or it will be a 12v signal that originates at the pushbutton controller. View the voltage at the switch in both off and on (working properly) condition and you will see which system you have.
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Continental Imports
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Last edited by stevebfl; 07-06-2003 at 01:33 PM.
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  #5  
Old 07-05-2003, 11:41 PM
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Join Date: Sep 2002
Posts: 134
Thanks stevebfl,
My car is deisel, and the signal is 12v (positive) at the low pressure switch if the ACC on...(from the CD, it says (-)) .....the problem is that this 12v is connected to terminal 10 input to klima and I did the test between terminal 10 (supposedly negative) and 5, which is positive => 12V...I am just confused how the positive is converted to negative...I might be missing something...

The main problem is the reading out of the compressor rpm sensor is not high enough (0.1 AC at idle)...this means that the klima receives this signal and thinks that the compressor is not working properly (compared to the engine rpm). If replacing the sensor would not help, what is the solution to this problem, new compressor (the comp. works fine if jumped)...
please help
thanks
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  #6  
Old 07-06-2003, 09:32 AM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
Below is the "klima hack" exhange which has become something of a classic. Hope it helps.

CT

GERMAN AUTOMOTIVE
Member
Posts: 15
FromALMDALE CA. U.S.A.
Registered: Mar 2000
posted 03-17-2000 03:44 PM
------------------------------------------------------------------------------
--
THE COMPRESSOR RELAY CAN BE BYPASSED AS FOLLOWS,USING RELAY # 001 542 02 19
MAKE YOUR OWN JUMPER WIRES. TERMINAL #1 ON KLIMA TO #85 ON ICE CUBE,#10 KLIMA
TO #86 ICECUBE ,TERM. #5 KLIMA TO #30 ICECUBE,AND #7 KLIMA TO #87 ICECUBE.
CLUTCH WILL ENGAGE AND DISENGAGE AT PUSHBUTTON ASSY'S COMMAND.M.F.
------------------
M.F.

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BRAD
Member
Posts: 11
From:SUMNER, TX 75486
Registered: Mar 2000
posted 03-17-2000 04:48 PM
------------------------------------------------------------------------------
--
THANKS TO GERMAN AUTOMOTIVE M.F. WILL THE COMPRESSOR STILL BE CONTROLLED BY
THERMOSTAT CONTROL WHEEL? ALSO WHAT ARE YOU REFERRING TO AS ICECUBE?
------------------
BRAD FRANCIS
1986 190D 160,000 mi.
SUMNER, TX

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Benzmac
Moderator
Posts: 3251
Fromuluth, GA, USA
Registered: Mar 99
posted 03-17-2000 09:11 PM
------------------------------------------------------------------------------
--
I have had to do this with 134 conversions because of the higher pressures.
It does work. The ice cube is a generic term for the Bosch 5 pin relay. You
can get one at any stereo shop... It will be controlled by the pushbutton and
will cycle on and off yes./.
------------------
Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #7  
Old 07-06-2003, 01:35 PM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Yea...what he said.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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