GK+ & GK- are the compressor speed signal inputs. The circuit 15 is key on battery power. Circuit 31 is always ground.
KL is the command signal that comes from the pushbutton control that turns the compressor on. That is a GROUND signal!
T is the signal that the engine is overheating, that also is a ground signal form a switch in the waterpump. Ground on T will shut the compressor off.
87 is the power to turn the compressor ON.
87Z is a command signal to the fuel computer to raise the idle.

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