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#1
07-03-2003, 01:29 PM
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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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#3
07-05-2003, 09:26 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
07-05-2003, 09:53 PM
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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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Steve Brotherton Continental Imports Gainesville FL Bosch Master, ASE Master, L1 33 years MB technician Last edited by stevebfl; 07-06-2003 at 12:33 PM.
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#5
07-05-2003, 10:41 PM
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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
07-06-2003, 08:32 AM
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Below is the "klima hack" exhange which has become something of a classic. Hope it helps.
CT GERMAN AUTOMOTIVE Member Posts: 15 From  ALMDALE 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. IP: Logged 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 IP: Logged Benzmac Moderator Posts: 3251 From  uluth, GA, USARegistered: 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
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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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