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  #1  
Old 10-01-2003, 08:26 PM
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87 300e air con problem, please can anyone help?

My 300e has the problem of latching off the air con sometimes, to re-start i have to turn the ignition off and then re-start the car, i know this is a safty feature that only merc`s seem to have down here in Australia. What i would like to do is ask your help to anyone who has the wiring diagram for the air con system and the knowledge to tell me what to briged out to by-pass the latching relay of this safty feature. (I`m sure it`s just a fauly sensor) and i just want to bypass it.
Cheers George.
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  #2  
Old 10-01-2003, 10:40 PM
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Actually that is a common problem, not a safety feature.
Try this, while the engine is running, turn the fan/ac on. If it does not comes on wiggle (slightly) the key in the ignition. Most likely the fan/ac will come on. That is worn contacts in the ignition switch.
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  #3  
Old 10-01-2003, 11:48 PM
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Thanks Pesuazo, been there done that, i should of listed all the things that have been checked, the only thing is a couple of thermistors at lurk apparently deep in the bowls of the dash, so my contact at merc Australia said and it`s big labour dollars to dismantel most of the dash to get at, that`s why he said to find the bypass answer, but he cannot tell me as it`s against his Mercedes Oath or something.
Thanks George. (there must be someone who`s bypassed this)
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  #4  
Old 10-01-2003, 11:53 PM
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Have you checked the belt tention? The 300E has a RPM sensor on the back of the compressor and if the belt slips the compressor will shut down and after restarting the engine will come back on.
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  #5  
Old 10-02-2003, 12:36 AM
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Yep, Stan done that too, done it all, the only thing is those pesky thermistors that you can`nt get to easily, or a faulty sensor somewhere, i`d rather just bypass the whole safety circuit issue.
Hell i`ve owned countless air conditioned cars that do`nt have this over enginered safety system, and i`m still alive to talk about it, it`s almost as stupid as to think that it could of been made by the British to put into a Jag or Rover or something British. ( i love the pommies, hell i was born in Oxford England) before any Brits overreact.

Cheers George
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  #6  
Old 10-02-2003, 01:07 AM
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If you remove the black plastic cover behind the battery you will see a black box marked "KILMA". Remove this module and take the cover off. On the circuit board there is a relay used to engage the compressor. I have seen the solder joints fracture over time due to heat and vibration. Resolder any solder joints that are not shiny or look damaged. This seems to be fairly common. Good luck.

Tom
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  #7  
Old 10-02-2003, 11:15 AM
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In my experience the most common cause of this problem is an excessive clutch air gap and/or grease & oil on the clutch. Check the clutch air gap with a common set of feeler guages, such as are used for valve clearance or spark plug gapping. It should be 0.50mm, with a variance of no more than 0.15mm. I find once it reaches 0.8mm the compressor cutout circuit begins to engage.

A simple possible fix is to just degrease the clutch. Get some aerosol brake cleaner (or similar) and spray it into the air gap to thoroughly soak and clean both surfaces. Sometimes this adds enough additional 'stiction' to avoid the compressor cutout circuit.

- JimY
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  #8  
Old 10-02-2003, 01:35 PM
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Another suggestion:
Try removing the CCU and retouching the solder points in the circuit board.That fix my AC/fan problems last summer
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  #9  
Old 10-02-2003, 06:27 PM
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Pesuazo, what is the CCU and where does it live. and TCG i will do what you suggest also, but i have had it out before i doubt whether it`s going to be the problem, but you never know.

But really guys we do`nt need the cut out circuit to be functioning, it`s problematic and needs to be bypassed, just read all the guys in the past that have had problems with it, and have spent a fortune trying to fix it. ,

Is`nt there and auto electrician reading this that has the work shop manual that can figure out bypass for this useless saftey feature.

Thanks George
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  #10  
Old 10-04-2003, 06:18 PM
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CCU
Climate
Control
Unit
Thats the one where the pushbuttons and temperature dial are in the car.
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  #11  
Old 10-04-2003, 07:07 PM
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To answer your question about a by-pass.

There are a number of threads giving actual pin numbers but here is the concept. The Klima is a smart relay that does what all relays do. It connects the clutch coil to battery voltage. Look to the bottom of the device and the power in will be term 30, power out is likely to be term 87. Verify that powering term 87 runs the compressor.

Your dumb relay will have to connect these two wires. The Klima receives its command signal from the PBC (push button controller) as a ground signal. So a properly wired 4 pin relay will have power on 30, output on 87, ignition power from a term 15 placed on term 86 and the command signal turning the relay on with a ground signal placed to the dumb relay term 85.

Before you waste a bunch of time verify the ground signal at the low pressure switch (the compressor on ground signal passes through the low pressure switch on the drier on the way to the Klima from the PBC).
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  #12  
Old 10-04-2003, 08:51 PM
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Thanks Steve, not as simple as just bridging out just two terminals is it, so i`ll study what you`ve said and do it when i have the relay and peace and quite from the wife and kids for a couple of hours.
I take it the system will still cycle with this mod, can you confirm this.
Cheers George.
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  #13  
Old 10-04-2003, 09:21 PM
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A/C prob

Ok i had a 300e doing that and it was too much distance between the clutch and the pully, all i had to do was take off the clutch and take out a couple off shims to make it closer to the pully and it worked fine after that. what was going on, was the clutch could not travel that far to close the gap and the control would not let it try again after that till i re started the car. hope this helps. you can look at the a/c clutch and see how much of a gap it has it should be real close if you can see daylight through it, it is too far apart..


Rob....
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  #14  
Old 10-10-2003, 03:02 AM
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O.K. guys for those of you who want to know how i went with all the advice,

TCG was the saviour, i picked his recomended fix to do first, because being a lazy beer swilling Australian i`ll always try the easier way first and leave the hard stuff for latter.

Yep the removal of the Klima Control Box, (by the way it should`nt be called a relay, because the small relay that`s inside it is only 10% of what it`s made up of the rest is all complicated circuitry with intergrated circuits and what not) anyhow i resoldered all the main contact pins then resoldered all the components on the circuit board, and now the air con WORKS!!!!! 100% perfect, yep it`s great when you`ve been lazy and gone the simple fix first and it was the answer to the problem.
Thanks to all who helped with their advice.
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