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  #1  
Old 06-05-2010, 12:47 PM
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'87 300 TD - A/C sensors, switches, klima, etc.

I am still trying to get the A/C working on my '87 300 td. The compressor has not been engaging - but I took it to Firestone this morning to do an A/C check. They checked it out and there was no freon (already had been converted to R-134) so they charged it up, and there don't appear to be leaks - but still no compressor function.

We did confirm that the compressor functions and appears to be okay by pulling the klima control unit and jumping the 5 to 7 pin hole. The compressor came on and we have A/C! It was good to know the compressor wasn't dead!

In the cd service manual (83-600.pdf) it lists compressor shut-down due to speed sensor, control unit, or microswitch. Also, online it was recommended to check the dual pressure switch.

I had ordered a Klima control unit - so I tried the new one - and still no luck. I have not located the microswitch (full throttle switch) - is anyone familiar with this model enough to explain where it is? ( I will keep looking)

Is there any way to bypass any of these sensors/switches individually to check to see if they are the one that needs replacement?

Are there any other possibilities I should also be looking into?

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87 300TD 230k mi's
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  #2  
Old 06-05-2010, 03:58 PM
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The Kilma looks for a lot of inputs to turn on the compressor - too complicated if one of the input signal is missing. I made a simple Kilma to have A/C and bypass everything. You can try this to get A/C first and fix the real problem later. Read my posts. Good luck.

300SDL Tach Issue
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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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  #3  
Old 06-05-2010, 04:24 PM
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If the Klima is working correctly, it needs a ground signal from the CCU to allow closing of the clutch relay coil.

So, pull the Klima and set the CCU on one of the buttons that will normally close the relay (the three buttons on the left).

If you get a ground signal at socket #10, then the CCU is good. However, I'm guessing that the CCU isn't providing the ground signal to the Klima. It's a typical failure mode of the CCU.
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Old 06-05-2010, 07:13 PM
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Thanks Brian - will check that tomorrow!

It definately could be the CCU - my first repair on this was the blower not working. I have the original blower motor, think it needed oil (was squeaking) it killed the regulator, and melted the housing for the single fuse for the blower motor. I replaced the regulator, and fuse and got the blower functioning again. I oiled the blower with wd-40 and got rid of the squeak, but I have noticed it coming back particularly at low speed. I think I am going to go on and replace it, unless there is something that will work tons better on oiling the bearings.
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  #5  
Old 06-06-2010, 05:53 PM
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Did I do this right?

Brian -

I am a newbie with testing out auto electrics. Wit the car running I did an ohm test from socket 10 to my ground (battery neg) and I got infinity rather than 0. I checked auto, low, and high fan to see. I zero'd the probes first by touching red to black.

I am assuming if I was getting a ground at 10 I would read 0 across that as it would complete the circuit.

If I did this wrong let me know.

Thanks!
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  #6  
Old 06-06-2010, 07:21 PM
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The CCU controls PIN 10. When it calls for A/C, PIN 10 goes LOW ( 0 Volt ). It is normally sitting at 12V, i.e. A/C off. You measure voltage, not Ohm. Switch DVM to voltage, clip the black probe to -ve of battery and the Red probe to PIN 10, then cycle the CCU to call to A/C to test.
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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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  #7  
Old 06-06-2010, 10:21 PM
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Quote:
Originally Posted by ah-kay View Post
The CCU controls PIN 10. When it calls for A/C, PIN 10 goes LOW ( 0 Volt ). It is normally sitting at 12V, i.e. A/C off. You measure voltage, not Ohm. Switch DVM to voltage, clip the black probe to -ve of battery and the Red probe to PIN 10, then cycle the CCU to call to A/C to test.
Unless the 124 is different, pin 10 will be grounded to close the relay for the compressor clutch. Accordingly, you measure resistance for confirmation.
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  #8  
Old 06-06-2010, 10:34 PM
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Quote:
Originally Posted by jmann.arch View Post
Thanks Brian - will check that tomorrow!

It definately could be the CCU - my first repair on this was the blower not working. I have the original blower motor, think it needed oil (was squeaking) it killed the regulator, and melted the housing for the single fuse for the blower motor. I replaced the regulator, and fuse and got the blower functioning again. I oiled the blower with wd-40 and got rid of the squeak, but I have noticed it coming back particularly at low speed. I think I am going to go on and replace it, unless there is something that will work tons better on oiling the bearings.
this is not oil.
it a very mild rust dissolver, and solvent.
you need to open it back up, and put some light grease, or oil on the bearings.
WD40 evaporates very quickly, and it attracts dust that will eat the bearings and the shaft.
get it out of there! I'd clean it off with electrical contact spray or brake spray, and dry it well, then pack it with light grease/wheelbearing grease.
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  #9  
Old 06-06-2010, 10:34 PM
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Threads like this do not make me look forward to getting my a/c working on my '87.... And to add insult to injury I rebuilt my wiring harness when I got the car... I have no idea if the a/c circuit in complete or not
Maybe my '87 will be a none a/c sport type car
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  #10  
Old 06-06-2010, 10:50 PM
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It's actually not all that bad, the A/C system. There are safety features built in, such as the Kilma comparing engine rpm to rotation of the a/c compressor, it disables the a/c clutch in the event of slippage or locking up. It saves the serpentine belt. You can do a search for icecube relay to bypass the Kilma. You can also bypass the pressure switch and temp switch with a wire. (For testing)
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  #11  
Old 06-07-2010, 12:51 AM
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$0.02

Quote:
Originally Posted by Brian Carlton View Post
Unless the 124 is different, pin 10 will be grounded to close the relay for the compressor clutch. Accordingly, you measure resistance for confirmation.
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.
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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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  #12  
Old 06-07-2010, 01:03 AM
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I pulled the wiring diagram (attached) for the 124.193 (300td) from 85 to July of 87 - the plate in the driver door says mine was built 11/86. The 10 socket path from the CCU (N22) to an engine cable harness (X26) to the pressure switch (S31) then to the klima control unit (N6). So - it still could be the pressure switch or any of the connections where I have lost continuity, but the CCU is the most suspect. I had pulled it out before hoping for charred wiring on the outside - but everything looked okay at the two harness connections.

Okay - at this point I could take the trim off to get to the kilma blindfolded. I can test voltage out too - but it seems like even if it is 0 v or 12 v which I didn't test - I have to have a resistance of 0 for it to be a complete circuit and I got resistance of infinity which essentially means some part of the wiring is fried going back from there. (correct?)

I have considered getting a dozen aligator clips with some wire to set up the klima control unit with wire extensions from the plug to the pins, and I could add an additional jumper from 10 to ground - which if the clutch engages - would tell me specifically that it is that circuit input keeping the clutch from engaging.

I guess the other good thing the wiring diagram showed me is the microswitch (s27/1) grounds right there adjacent the battery at w10 - so it should be right there between the battery and klima relay.
Attached Files
File Type: pdf 83-606_124-193_to_july_87.pdf (175.9 KB, 143 views)
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  #13  
Old 06-07-2010, 01:14 AM
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Quote:
Originally Posted by jmann.arch View Post
I pulled the wiring diagram (attached) for the 124.193 (300td) from 85 to July of 87 - the plate in the driver door says mine was built 11/86. The 10 socket path from the CCU (N22) to an engine cable harness (X26) to the pressure switch (S31) then to the klima control unit (N6). So - it still could be the pressure switch or any of the connections where I have lost continuity, but the CCU is the most suspect. I had pulled it out before hoping for charred wiring on the outside - but everything looked okay at the two harness connections.

Okay - at this point I could take the trim off to get to the kilma blindfolded. I can test voltage out too - but it seems like even if it is 0 v or 12 v which I didn't test - I have to have a resistance of 0 for it to be a complete circuit and I got resistance of infinity which essentially means some part of the wiring is fried going back from there. (correct?)

I have considered getting a dozen aligator clips with some wire to set up the klima control unit with wire extensions from the plug to the pins, and I could add an additional jumper from 10 to ground - which if the clutch engages - would tell me specifically that it is that circuit input keeping the clutch from engaging.

I guess the other good thing the wiring diagram showed me is the microswitch (s27/1) grounds right there adjacent the battery at w10 - so it should be right there between the battery and klima relay.
This is what you need to do.

1) remove the Kilma relay.
2) Use a DVM and connect black probe to battery -ve or chassis.
3) Connect/Insert red probe to PIN 10 of relay socket.
4) Start the car and turn OFF A/C. You should read 12V on DVM
5) Turn ON A/C and you should read 0V.
6) Disconnect pressure S/W at recv/dryer. It should read 0V as CCU turns off A/C
7) If everything checks out OK above then the CCU is OK.

There is nothing to lose to do the above, everything to gain.
__________________
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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  #14  
Old 06-07-2010, 01:22 AM
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oil da bearings

on the motor -

vstech -

I kinda realized after that the wd-40 was a bad idea - particularly now when the fan on low squeaks. I didn't have anything on hand at the time. I was thinking sewing machine oil, or a mineral oil. There really isn't even a spot to add oil. I looked for a hole or anything around the shaft to get more directly to the bearings. I don't think there is any way to pack them with grease - more likely just a light oil. Ooo - just realized I have some light oil for the toy train set that would work. I'm pretty sure I have break cleaner to clean it up - but with the squirrel cage fans on the shaft the best you can do is oil the shaft right next to the bearings on each side.

This will be the fourth time I have gotten in to the fan in the last six weeks. I'm getting really good at it. It helps to remember to reconnect the wiper blade plug, and to finish all of your diagnostic the first time!
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  #15  
Old 06-07-2010, 01:40 AM
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ah-kay -

I can give that a try - but to get to the pressure switch I have to remove the SLS hydraulic oil resevoir, as the switch and receiver/dryer are underneath it. I can't see any lines coming out the bottom of it, but there has to be something. I am assuming I can plug all the holes and disconnect it for a few minutes to get to the stuff below. Any alternate suggestions?

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