sends a voltage signal to the ECU. I did hunt that pin down and connected it to ground using a DVM. The voltage did go up but less than 12VDC. Been a while so I don't remember excatly the value. Every time the clutch cycled off and the a/c stopped cooling, the line went hot. Using a digital thermometer this occured at 44F. No wonder cooling is poor.
I did notice the lower price of the XTerra TCA. The Z32 is $120 (minus shipping). Is it possible that the grounding function is a modern feature? I have no idea how the XTerra controls its a/c, and I am still puzzled why, the Z32 involves the ECU when the a/c has its own "box".