KLIMA Basics missing from this forum

[carock]

Were you able to get the AC clutch to operate at idle speeds under 800 rpm with the EGR computer removed? I think the Klima or the EGR computer has some function to increase idle speed when it falls below 800 rpm with the AC on.
Either way, my 1985 300CD with the EGR computer bypassed and rewired for a working tach signal will disengage the AC clutch at speeds exactly under 800 rpm. If I adjust the idle to be over 800 rpm with the AC on, then the idle speed will be about 950 rpm with the AC off. I am still trying to figure out if this can be fixed. I disconnected the brown/red wire at the #4 Klima pin, but this had no effect.

[ykobayashi]

My AC in the 85 300D stopped working. I traced the issue to the Klima relay. I have good climate control command signals and tach. I was able to jump the compressor relay in the Klima and get my AC to work.

Obviously the problem is somewhere in the Klima box. I butchered the box and bypassed the compressor relay with a lamp relay commanded by KL. So when I hit my AC button on my CCU the compressor turns on.

Basically the Klima controls the AC compressor for some conditions like shutting down when the engine is starting (via rpm). The rest of the switching like pressure, temperature, evaporator Temperature, and accelerator kick down are all handled through a wired series circuit upstream of the KL line outside the Klima.

I think I had all the inputs right but my Klima was just dead. I had signal on KL but the relay that activates the compressor was off. Something was not allowing it to turn on. My gut feel after probing around a bit is it is in the Klima relay and not an issue with the car. I have a good OVP relay, good tach and functional EGR computer.

In the past I reheated the old solder on the Klima and that got my AC working. I tried that this time to no avail. All the connections are good. I think there is an issue in the circuit board. I went through and tested every diode, transistor and capacitor and they are all good. That leaves the big ICs in the Klima. COP411L and the LM393 comparator and a National Semi PLL chip (forgot the number but it was an old classic with a VCO, phase detector etc.).

I looked up the PLL and that looks like how the Klima monitors the tach signal. Likely locks on to the tach signal to provide a measurement of crank rpm. My recollection is the compressor wasn’t supposed to turn on when you crank the car to make it easier to start but once the engine lights off the compressor relay gets activated. Forgot where I read this so correct me if I’m wrong.

The COP411 is shockingly a 4-bit RISC microcontroller. It’s a full out computer designed in the Stone Age. 512 instructions of memory. That’s 1/2 a K of instructions for the nerds out there. I guess this was something to use in 1985 to monitor a bunch of inputs from the car to decide on a single output = compressor on/off signal.

So I really couldn’t find what was wrong with my relay except that it was internally deactivating the compressor. My guess is it was malfunctioning and it decided to mistakenly deactivate the compressor. I used Brian Carleton’s thread to wire in a 12V lamp relay to use the CCU signal KL to activate the compressor. Simple stuff. Works now. Tossed the board and only used the pins and outer shell of the Klima.

https://www.peachparts.com/shopforum/959239-post51.html

I had a slight issue with Brian’s wiring and used a separate ground from the input coil ground to KL. Somehow the way Brian does it turned my relay into a doorbell buzzer due to feedback. Disconnecting thr doubled up line and splitting the signals solved the problem.

Just thought I’d share the info. Luckily Programma sells a rebuilt Klima or offers rebuilding service for those who want to keep their car original. It was a little expensive at $190 so I just rolled my own with a lamp relay.

[Mxfrank]

Klima handles a lot of barely related functions, including activating transmission kickdown, controlling a/c based on RPM, protecting the belt system if the a/c clutch fails, other odds & ends. I worked out a way to maintain most Klima functionality using two relays. It's more complete than the single relay approach, but still can't deal with the speed sensing functions: https://www.peachparts.com/shopforum/diesel-discussion/386849-compressor-speed-sensor.html#9

[vwnate1]

THANK YOU for all this information ! .