Klima problems on '85 TD
 

I have relentlessly been tracking infro on Klima relay problems on my '85 300TD.
Have read the relevant posts, but need a few pieces of practical info from soneone who has been there.
I have both 12v dc and the 12v control signal from the ccu at the Klima socket. The control signal goes off when the ec button is pressed, and comes on again for any of the other options, including, for some reason, defrost.
So, if I have 12 volts to kick in the compressor clutch and 12 volt control signal, I should be able to jumper the relay and get the compressor running, right?
My questions: Is there another Klima board, behind the battery, let’s say, on the '85 TD. or are all the Klima circuits built into this $240 relay? What else does this Klima relay monitor or control? I understand the '85 circuit on the 123 is different from all others, hopefully less complex
Which pin on the relay socket controls the compressor clutch? I don't want to backfeed 12 volts into a solid state circuit in the wrong polarity.
As with my 84 123, when I jumper the hot pin to the compressor clutch, the clutch should engage for a test.
I need to make this simple test on the 85 to decikde whether to replace the Klima, tear it apart for a rebuild, or simply replace it with a much simpler ice cube relay. My experience is that inept probing with a hot 12 volt line can do some damage.

To defrost the windshield you have to dehumidify the air too. The compressor is designed to come on when the defrost button is pressed.

Is the compressor clutch pulling in when you "jumper" the pressure switch?

Yes, the 85 is totally different from the earlier compressor control. The earlier 123 cars do not have a Klima relay.

The Klima relay looks at engine speed, temp, voltage, and full throttle to decide whether to fullfill its command to turn the compressor on.

No, the compressor does not kick in when I jumper the pressure switch. That would be too easy. The compressor, clutch and receiver/dryer are all new, as are the switches. I have positive 12 volts at the switch and positive 12 volts from the ccu at the Klima socket.
Does the Klima switch positive or negative? If I need to bypass the Klima, which pins do I jumper to get the compressor running.

The fact that you viewed some terminal changing volyage when you went from EC to any other position confirms you have the "comp on" signal at the Klima.

The 87 terminal is probably the terminal that will be hot when the clutch is engaged. If you don't have a bad Klima then you have a bad signal from: engine speed, temp, voltage or throttle position.

Does the tach work?

No, the tach doesn't work. But the a/c was working without the tach as soon as the new stuff was installed. My parts supplier tells me the tach does need to work in order for the a/c to kick in on this model.
I really do not need all the bells and whistles the Klima is supposed to offer. The pressure switch will protect the compressor. I have wired the aux fan directly into the compessor blue lead.
I do need a/c. Any ideas on which pins to jump to get the a/c clutch on. Then I can work backwards to wire in an ice cube relay that will kick in the clutch. Simpler is better!

Well I could tell you if I were looking at the relay. My guess is 30 in 87 out to the compressor. The control circuit will be 86 or 85 depending whether the control is 12v or ground. The other 85 or 86 will be the complement.

Thanks for the comeback. I have tried jumping positive 12 volts from the battery to each terminal of the Klima socket. Nothing at the clutch.
Does this mean the control circuit is negative, and that the brown (ground) is being switched?
The Klima relay easily comes out of its case, as though someone else has been probing the innards. When I install the Klima and manually close the two small relays on the board, again, nothing happens. It appears that relays are normally closed and that power opens them both.
It also appears that not all the positions on the pc board have been filled. My parts supplier tells me that this model 85 300TD does not use a signal from the tach to control the compressor.
When I apply 12 volts positive to the relay socket, I can hear the blower start at one pin, and a relay clicking at another, although it is not the compressor.
What conclusions can I draw from these obserations?