air conditioning diagnostics

[420sel man]

We got enough time off for a trip to the beach, had a great time till we got in to come home in our 89 420 SEL. No AC... It had worked fine up to that point. I have spent hours reading old posts trying to educate myself. Also have spent several hours with the repair CD.

Here is what I have checked or found so far:
Power through all fuses.
Shorting the pressure switch on the reciever dryer makes no change.
Compressor is not turning.
When defrost button is depressed, compressor still does not start
If temp select wheel is turned to red, blower blows hot; if set to blue, temp is ambiant.

Last winter I noticed that the blower would start blowing before engine was up to 33 degrees C, so I have been searching for the cold engine kill switch, but have not found a single pole sensor to test. I did however find a 4 pole sensor between the distributor and the air horn/meter body. Unable to find any reference to what this sensor is. ??????

I have located the single pole temp sensor for the gauge and the two pole sensor for the fan.

I have located the klima relay # 002 545 18 05

Can some one help with figuring out which part in this circuit needs replacing or repair

many thanks!!!!!