87 300SDL --- weird, erractic AC issues - PeachParts Mercedes-Benz Forum

ah-kay · #10 05-02-2012, 11:29 AM

Quote:

Originally Posted by daw_two

So, I attempted to build a simple ice cube relay to control the AC compressor with just the ACC thermostat wheel. After that failed (I guess there's a reason why I'm not an Electrical Engineer), I kept staring at the KLIMA relay that I have from that 1991 350SD parts car. I turned it over and saw the labels on the pins --- they are the same as the 300SDL. Plugged it in and cycled the key and ACC unit and presto, I have working AC.

I did test to see if jumping "hole" 5 & 7 and sure enough that powers up the compressor without any protection.

Oh.....btw....after I turned the car off, I remeasured the resistance between "hole" 9 & 11 (speed sensor) and measured 707 ohms. I'm guessing the range of 530 to 650 ohms is a cold measurement.

So, it looks like my existing KLIMA relay was the culprit.

Anyone want to give me a lesson in reading/interpreting the KLIMA relay diagram?

Good job. I do not realize that you have a 19i91 SD parts car. The Kilma should be compatible. So the time I spent last night to hack the Kilma circuit and PM'ed you was all in vain.

The problem is the Kilma, not the speed sensor in the compressor. Speed sensor rarely goes wrong unless it is open circuit. The speed sensor measurement is done by a IC differential circuit. One cannot fix it unless one knows the part number.