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  #16  
Old 06-07-2010, 01:52 AM
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You can skip step (6) as I am not familiar with the placement of the recv/drier of your car. I am surprised it is so difficult to get to. My suggestion is to check the functionalities of the CCU. Monitoring the freon pressure by the CCU is to protect the compressor, it would be nice to know but it is not absolutely necessary for now. I want you to confirm the CCU can toggle the signal and eliminate it from the diagnosis.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.
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  #17  
Old 06-07-2010, 06:36 AM
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Quote:
Originally Posted by ah-kay View Post
The CCU is active 'low' to turn on A/C. How you measure it is up to you. However, you can only measure resistance UNLESS you have something connected, that is the Kilma replay is plugged in. If it is plugged in then you need a mean to get to the PIN underneath the relay, like an extension card. The resistance is not going to work well as the relay on/off can be overrided by other inputs. The simplist way is to measure the voltage toggling when the CCU call for A/C. The CCU monitors the freon pressure so if it goes low ( 0 volt ) then you know the CCU is in good shape.

There is nothing to it in MBZ A/C circuit if you understand simple electronics. Kilma relay is nice as it can protect the serpentine belt, turn off A/C when over-taking etc. However, when it goes wrong, it takes a lot of effort to diagnose the issue.
As previously mentioned, none of that is accurate for a W126. It receives a ground signal from the CCU to close the compressor clutch. You do NOT need the Klima plugged in. You simply look for continuity to ground when the CCU calls for the compressor to engage.

Gassers are definitely different and function with voltage on that socket as you have described.

The W124 may function like a gasser............but, I'd be absolutely sure before posting here with a test that has the opposite logic from other diesels.
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  #18  
Old 06-07-2010, 10:39 AM
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CCU/Computer controls voltage to switch something on/off. It can be active low or active high. If it is active high then the CCU will provide the current. If it is active low then it will sink the current. They do not control resistance. This is electroniics 101. However, the voltage is used to drive something like a relay or a light bulb. So you can measure resistance or current as long as you know what you are doing. I have fixed all the Kilma on all my 300SDLs so it not as difficult as it seems.
__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Last edited by ah-kay; 06-07-2010 at 11:45 AM. Reason: typo
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  #19  
Old 06-07-2010, 06:12 PM
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Quote:
Originally Posted by ah-kay View Post
CCU/Computer controls voltage to switch something on/off. So you can measure resistance or current as long as you know what you are doing. I have fixed all the Kilma on all my 300SDLs so it not as difficult as it seems.
The above is factually incorrect for a W126.

The CCU provides the GROUND to close the clutch relay in the Klima.

If you fixed your own Klima's on the W126, it had nothing to do with the ground signal from the CCU and you are requested to refrain from posting any more erroneous information as others depend on it.
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  #20  
Old 06-07-2010, 06:45 PM
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Providing ground means the volt is switched to chassis, 0, ground. The CCU is sinking current from the source in electronic term, so to speak. Call it what you like, you can mesaure resistance all day long if it matters to you. We are moving to 40 nano meter circuit now, not discret components back in the good old days.
__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.
Reply With Quote
  #21  
Old 06-07-2010, 06:53 PM
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Location: Blue Point, NY
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Quote:
Originally Posted by ah-kay View Post
Providing ground means the volt is switched to chassis, 0, ground. The CCU is sinking current from the source in electronic term, so to speak.
Incorrect again.

The CCU switches from open to battery ground.

There is no "sinking of voltage".

I'm going to ask you one more time to refrain from posting further on this thread as it's obvious you have no understanding of the function of the system.
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  #22  
Old 06-07-2010, 06:55 PM
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I wrote 'sinking current', not sinking voltage. Please google the term for your info. I am getting out as this is 2010, not ice age.
__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.
Reply With Quote
  #23  
Old 06-07-2010, 07:05 PM
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Originally Posted by ah-kay View Post
I am getting out
Excellent.

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