The AC works good but once in a while its stops cooling. The solution to getting it to cool again is to turn off the key switch and back on again. After the key switch is turned back on, the AC cools fine again.

Has anyone else seen this problem? Any suggestions why it does this?

P E H

Funny thing. I fired up the SD the other day and when I left the AC cooled fine for about the first 10-15 minutes of driving and then warmed noticeably. Haven't tried it again recently.

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

the a/c compressor has a speed sensor on the back of it, if the speed varies due to belt slippage or if the compressor may start to sieze it will disengage the a/c compressor clutch or if the rpm sensor it's self is bad the a/c klima relay may disengage it due to a bad signal.
also the pressure sensor on the reciever dryer may be defective.

I have the same problem with my '87SDL; occasionally (once a month, maybe) the compressor cuts out due to what I believe is the speed sensor signal to the Klima. Always comes right back on when I re-start the car; this is how the manual says the speed sensor/klima is supposed to work when an RPM mismatch is detected. Ray's info is spot on. I can't re-produce the problem in order to debug. I suspect it could be caused by one of the following:
- clutch gap
- compressor going out
- belt or tensioner (mine are both new)
- compressor speed sensor
- klima

as ever
Paul

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as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5

Well, now I've also got the trouble.

But, it now cuts the compressor out within three minutes, every time the vehicle is started. Very repeatable results.

Compressor works fine and cold air is produced. Then, about three minutes later, it drops off line.

Are there any procedures for checking that speed sensor. Can it be jumped in any fashion to confirm that it is the culprit?

I did cause the sensor to cut out about one month ago when I drove through heavy standing water and, apparently, caused the belt to slip.

Maybe the sensor is now damaged?

On the 126 CD, in the ACC section, there is a 1986 Suppliment which has a section on testing the compressor cutout (Klima, speed sensor, etc). I can email this PDF if needed. I've run thru the tests on my car and can find no anomolies, yet I still have an occasional compressor cut-out.

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as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5

speaking of A/C. i've been having the hardest time trying to find R12. about 2 days ago i found a jusnk yard that carries an R12 replacement. it's 9.0oz a and $15 per can. will this work?
also would anyone here happen to have a wire diagram for an 86 300sdl instrument cluster tach?

thanks

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ez rider

Paul, I don't have the climate control manual for the W126, so, if you could e-mail me the relevant section for testing the Klima, etc., I be very appreciative.

TIA

I have the hard copy of the electical troubleshooting manual. I could make a copy and send it to you.

Unless you need a specific question answered that I could do via the forum.

thanks a million

i do have a specific question.
i would like a diagram for the wires going into the instrument cluster.
EXAMPLE
RED goes to pin 12
Blue goes to pin 15 etc.

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ez rider

This would be better done by the schematic. There are a ton of wires to the cluster.

I'll make a copy of the relevant pages and send them to you.